what comes before the merge?

[SeeM]

Area most free of debris & beyond proximity limit.
[...]
2.  "Jump in beyond Pluto" sort of thing but on the same planetary disk.  Runs the risk of debris
[...]
This point has more risk of debris as not everything in the system is orbiting on the planetary disk

Debris is moved out of the way by introducing annihilation to some kilograms of matter at the arrive point, which is converted to energy, leaving very energetic radiation for a short time. It would clear some dust, but unfortunate ice ball still could do a lot of internal damage and kill the crew.

[EPG]

I think it would largely be a personnel issue.  The further out you go *(and the zenth/Nadir points are as close as you can reliably come at acceptable risks for a jump operation with massed transports) the furtehr out you hae to start decelerating, the longer it's going to take, the higher your chance that some portion of your forces will do s omething catastrophically stupid or unproductive.  also the more fuel, air and water you have to pack for the trip.

The most important thing to an invasion  planner, is getting their invasion forces into a position, in a condition, to conquer the target reliably.  (hence, why Kerensky needed to secure the zenith and nadir points instead of going off-axis or through pirate points.)
 
Hyper disciplined troops, with large ships that have extensive room for exercises and a strong logistical tail, could manage an off-axis invasion and bypass the 'predictable' route-if they have ample time to spend, ample budgets, etc.

The typical robot-cowboys we see in the fiction, representing elites? not so much.

These are all good points and I agree with them. Another one is that any real sustained attempted invasion (not a raid) is going to require continued sustainment and resupply coming in from out of system with parts, replacement crews, follow-up invasion units, occupation troops, replacement equipment, specialists and special equipment that wasn't initially expected, major hospital and injury stabilization and triage facilities, in system R&R (either transported and set up on planetside if it's safe to do so, or in orbit if it's not) civil affairs and police to manage the conquered portions of the populace etc. 

For the initial 'spearpoint' of the invasion achieving some level of surprise via a super long range jump point or pirate point might be workable, because they are getting the elite navigation crews with top maintained (or new) jumpships to hit that pirate point reliably, or they are those hyper disciplined assault teams in 1/2 full dropships specially modified for the mission to allow for improved crew habitability as they spend 3-4 weeks burning in to their drop points.

For everyone else, you need at least semi reliable arrivals and departures making trips to and from the planet which are reasonably short and predictable, and for 'normal' crews and equipment in fully loaded transports to be able to make the trip safely and efficiently.   To do that, you really really need those stable zenith and nadir points. Enemy action, breakdowns, miscommunication, the inevitable shortages of transport and equipment ('you mean they really need 250 full scale water purification systems with 100% spares backup within 4 weeks to keep going? I never thought they would be able to poison ALL the water supplies on a continent on such short notice' '75% of our inferno bombs have defective arming fuses because they got subcontracted out to Quikscell - we won't be able to effectively prevent their scouts from figuring out what we are up to without them' 'the spacers navigation guild says they are going to initiate a 1 week shutdown on Sunday if we can't guarantee their safety in the invasion zone according to the following demand letter' ) and the normal 'friction' of managing a campaign on such a large scale is going to create enough problems as it is.

[Hellraiser]

These are all good points and I agree with them. Another one is that any real sustained attempted invasion (not a raid) is going to require continued sustainment and resupply coming in from out of system with parts, replacement crews, follow-up invasion units, occupation troops, replacement equipment, specialists and special equipment that wasn't initially expected, major hospital and injury stabilization and triage facilities, in system R&R (either transported and set up on planetside if it's safe to do so, or in orbit if it's not) civil affairs and police to manage the conquered portions of the populace etc. 

For the initial 'spearpoint' of the invasion achieving some level of surprise via a super long range jump point or pirate point might be workable, because they are getting the elite navigation crews with top maintained (or new) jumpships to hit that pirate point reliably, or they are those hyper disciplined assault teams in 1/2 full dropships specially modified for the mission to allow for improved crew habitability as they spend 3-4 weeks burning in to their drop points.

For everyone else, you need at least semi reliable arrivals and departures making trips to and from the planet which are reasonably short and predictable, and for 'normal' crews and equipment in fully loaded transports to be able to make the trip safely and efficiently.   To do that, you really really need those stable zenith and nadir points. Enemy action, breakdowns, miscommunication, the inevitable shortages of transport and equipment ('you mean they really need 250 full scale water purification systems with 100% spares backup within 4 weeks to keep going? I never thought they would be able to poison ALL the water supplies on a continent on such short notice' '75% of our inferno bombs have defective arming fuses because they got subcontracted out to Quikscell - we won't be able to effectively prevent their scouts from figuring out what we are up to without them' 'the spacers navigation guild says they are going to initiate a 1 week shutdown on Sunday if we can't guarantee their safety in the invasion zone according to the following demand letter' ) and the normal 'friction' of managing a campaign on such a large scale is going to create enough problems as it is.

Colorful & agreed.

A good invasion isn't going to be just 1 initial thrust either.  For example.

Lets say Taskforce-A is a Monolith jumping into a Pirate Point & releasing the 1st 2 Mech Battalions & some Spec Ops Infantry & a Fighter Wing.
Sooo,  Overlord,  Union x2,  Leopard x3,  Vengeance,  Fury,  Seeker.
This force jumps in first & is designed to give minimal warning to the enemy, they are 18 hours out from the planet when they arrive.
Initial targets are radar & communications relays & then the space port.

Taskforce-B is a single Merchant jumping into the Nadir where there is an Olympus Space Station.  (Communication from Planet to SS has a 45 minute lag)
They arrive 14 hours after TF-A with a Monarch & Buccaneer & are using faked codes to appear as a civilian hauler.
They request cargo/passenger transfer with the space station but when the DS dock w/ the SS a Battalion of Marines storm the place.

Taskforce-C is a Trio of Invaders that show up 6 hours after the Marines of Taskforce-B.
They have an Excalibur, Fury, Intruder, and a pair each of Mules, Triumphs, & Condors.
TF-C has the remains of the Mech Regiment, the Artillery Battalion, about 2/3 of the Armor Brigade, & 3/5 Regiments of the Infantry Brigade of the attacking RCT.
TF-C arrived later to allow A & B to cut off communications between each other hopefully w/o either location getting warned that the system is under attack.
TF-C conventional units will split & hold early gains while others support the advance of the Mech regiment.

Taskforce-D is slated to be the 3rd wave, after TF-A/B JSs leaves the system & jumps back to the launch point & will pick up the remaining 3 regiments of the RCT as well as another oversized mixed brigade of Tanks/Infantry that will assist in conquering the rest of the planet.  But it will be 3 weeks before they arrive back in system.
TF-D & all later waves will keep using the Standard Nadir JP & the newly secured Olympus Station.

[EPG]

Colorful & agreed.

A good invasion isn't going to be just 1 initial thrust either.  For example.

Lets say Taskforce-A is a Monolith jumping into a Pirate Point & releasing the 1st 2 Mech Battalions & some Spec Ops Infantry & a Fighter Wing.
Sooo,  Overlord,  Union x2,  Leopard x3,  Vengeance,  Fury,  Seeker.
This force jumps in first & is designed to give minimal warning to the enemy, they are 18 hours out from the planet when they arrive.
Initial targets are radar & communications relays & then the space port.

Taskforce-B is a single Merchant jumping into the Nadir where there is an Olympus Space Station.  (Communication from Planet to SS has a 45 minute lag)
They arrive 14 hours after TF-A with a Monarch & Buccaneer & are using faked codes to appear as a civilian hauler.
They request cargo/passenger transfer with the space station but when the DS dock w/ the SS a Battalion of Marines storm the place.

Taskforce-C is a Trio of Invaders that show up 6 hours after the Marines of Taskforce-B.
They have an Excalibur, Fury, Intruder, and a pair each of Mules, Triumphs, & Condors.
TF-C has the remains of the Mech Regiment, the Artillery Battalion, about 2/3 of the Armor Brigade, & 3/5 Regiments of the Infantry Brigade of the attacking RCT.
TF-C arrived later to allow A & B to cut off communications between each other hopefully w/o either location getting warned that the system is under attack.
TF-C conventional units will split & hold early gains while others support the advance of the Mech regiment.

Taskforce-D is slated to be the 3rd wave, after TF-A/B JSs leaves the system & jumps back to the launch point & will pick up the remaining 3 regiments of the RCT as well as another oversized mixed brigade of Tanks/Infantry that will assist in conquering the rest of the planet.  But it will be 3 weeks before they arrive back in system.
TF-D & all later waves will keep using the Standard Nadir JP & the newly secured Olympus Station.

Yep - love it.  And if it works, it won’t be until they properly detect task force C that they realize this is anything other than a raid, or maybe even when force D jumps in if there has been a little confusion/misdiection, etc to muddy the waters.