Hey Omega!
So this may seem to go against many folks interpretation of the lore here. But in truth, it's your game and your the narrative author of it. So it's really what you and your players deem as the most fun for your time and effort. But I personally say to go against the norm of the cannon 4 mech lance composition. Whose to say that there wasn't an irregular unit (or twenty) out there that somehow fielded more than your standard 4 mech lance before the clans invaded?
There literally are thousands of worlds and tens of thousands of units and hundreds of thousands of reasons for them to exist. The only difference between you as a GM and the writers and designers of this game is that they took the time and put in the effort to get their ideas published as canon... so the choice is yours to make what you feel like can become your canon to your game development. Design your universe and your interpretation of the Battletech/Mechwarrior universe around the ideas that work for you, your gamers, and their crew.
In theory, if you wanted to up the unit size a bit to say the size of a Union dropship
http://www.sarna.net/wiki/Union, you could then have each player control perhaps two or three mechs or other onboard assets (aero, vehicles, infantry, artillery, perhaps even power armor if you wanted to be a little ahead of canonical time frame) while on the tactical battlefield. That way it gives them a bit more than just their primary character to deal with and it gives them a sense that this is their unit as a whole. Of course the more you allow them to have the more it means that you have to prepare for and consequently get them to understand how to play the game in detail with. But in truth, a combined arms unit is the best approach as it gives you quite a bit of flexibility for a long term campaign.
If you wanted to keep the unit really small, then perhaps using a standard Leopard dropship which carries 4 mechs and 2 aerospace fighters is the best approach...
http://www.sarna.net/wiki/Leopard. With that thought in mind, you could, in theory, remove the 2 aerospace bays for a 5th mech bay, similar to the Clan's Broadsword dropship...
http://www.sarna.net/wiki/Broadsword. Or perhaps instead of removing the 2 aerospace bays on the Leopard have your last player play them or use LAM's (Land, Air, Mechs) or some other combination of ground, helo, hover, power armor, or WiGE vehicle bays and equipment. You could also make this small Leopard dropship sized element a part of a larger unit and the players just have control of this small asset whereas you as the GM narrate the rest of the units happenings.
Anyway... I hope that helps a little for the lance/unit idea!
As for the number crunching and stats tracking for your NPC's. I suggest that you wing the stats for NPC's as much as possible but do have some notes and stats onhand of the major movers and shakers that are going to be apart of the game on a regular basis as well as a list of generic names that you can use on the fly. Be realistic in the NPC's stats (attributes, skills, special abilities, and positive and negative traits), the better they are as NPC's the more flaws and drawbacks they should have built into them to offset the positives. But you literally do not have to stat out every character by the book. A good rule of thumb would be to look around here on the forums for some folks ready-made character ideas which many have posted.
Another small suggestion is to get yourself familiar with the out of mech combat system as well if you are not familiar with it. A gentleman by the name of BiggRigg42 here in recent forums post put some effort into a YouTube web series to try to teach the basics of the game to players and GM's alike. Which ideally works for some to learn the game easier than it does for someone for the first time sitting down to read a stat crunching digest of a book. I personally suggest that you and your players take the time to watch them even if you are familiar with the system but haven't played the game in a while as he is fairly spot on with the minutia of how the mechanics of the system works and his web series can be watched in about an hour.
BiggRigg42's Mechwarrior Tutorials...
https://www.youtube.com/watch?v=stw13oZLpYQAs for story plots and ideas... well my suggestion would be that depending on how you plan to introduce the idea of the clans in time to the party. Then perhaps maybe that's why this unorthodox units creation was brought into the fold of your game universe by breaking that perceived tradition of the 4 mech lance norm that everybody else gravitates too. Remember, just because you have 1 particular NPC in mind with the forethought and knowledge of the clans upcoming invasion, perhaps there can be others in the background whom see the writing on the wall as well and want to start by training up an experimental combined arms unit that employs a 5 mech or more composition that can break that old stoic mold.
The big thing to bear in mind is the learning curve of the number crunch of the tabletop can be offputting to new players! And as you said... some of your players are not fond of it and are new to the game. So do the math for them and let them learn as they go. Don't force them to do it for themselves in the beginning or they'll resent you for it. If the players want more of the Game of Thrones style skullduggery then go with that. If they start to love the tactical tabletop side of the game then do more of that. If they see themselves as the breaking and entering, blowing stuff up special forces types, or some other movie or TV Tropes, then go with that and adjust your campaign design as needed to keep the gaming fun and alive hopefully for many sessions to come.
Lastly, I'll end my thoughts for help with the shout out to two great YouTube / Twitch web series for thoughts of adventures by suggesting that you and your players take some time and watch and listen to the ongoing Battletech / Mechwarrior campaigns by these great folks.
APGamingReal's Battletech A Time of War - his live episodes are on Thursday evenings on his Twitch channel and he does have a discord as well.
APGamingReal's YouTube channel...
https://www.youtube.com/watch?v=JrTXHDjQja4&list=PLOTilBK2SqLP5BsH8kWSTzF3DIyudCrunAPGamingReal's Twitch channel...
https://www.twitch.tv/apgamingreal/videosand the other game is from the Hyper RPG folks called "Death From Above" though after a few seasons some of them broke off from the Hyper RPG crew tag and now they have their current live episodes on Saturdays afternoons on their new Twitch channel called ZombieOrpheus.
Death From Above on YouTube...
https://www.youtube.com/watch?v=hhrDrkfUYvs&list=PLHKocVDXoWBvk0-skvvtUaMiFoo1MYPd9Death From Above on Twitch...
https://www.twitch.tv/zombieorpheus/videos
Also... I've personally found usefulness in some of our good community memberships own personal character sheet creations here on these forums who have excellent automated excel character sheets designed for helping to create fully fleshed out characters easier and faster. I've attached one such finished PDF character sheet from me to you and a blank version of the automated character creator designed from a gentleman by the name of Gigobyte, as well as his instructions on using his excel sheet. By the way, it's best to download the character creator to see and utilize its full functionality rather than to try to use or view it as a web document in whatever web browser you are using. As far as functionality of his sheet, once you get to understand it and operate it, then it shouldn't take you long to make a character using it. The only thing about his sheet that I see as a drawback is that since the Mechwarrior game is a very skill heavy laden game and that there literally is a limit to how many skills that will physically print in the character sheet section of the sheet. You'll see, it's a little more than 50 skills that it is capable of printing. After that, it cuts them off on the printed sheet when in reality the character that I'm providing a link too, Kadan Van Zandt, in the PDF copy actually has about 5-6 more skills listed that are only in his character creator. You'll understand what I mean when you test it for yourself.
I want to say there are over 75 skills or so to this game with some of them having upwards of a dozen sub-skills. Unfortunately, I've seen no automated or fillable character sheet anywhere else on the internet that will be able to print all of them that you want to be listed on one simple character sheet. But this is as close and as good enough that I've seen as acceptable and have since learned to accept and adapt it to my GM'ing style and my players have learned to appreciate, enjoy, and use it for themselves.
One recommendation that I found in gameplay is to consolidate the skill lists into their parent list. Such as trying not to force a player to take different versions of the base skill. Take the Protocol, Streetwise, or Survival skills for example... if you keep it a general skill roll and then apply a common sense approach to the bonuses and penalties you assign depending on just how well the character truly knows the area they are in then it makes more sense than forcing the player to spend experience on each and every subskill. Here are the sheets!
Major Kadan VanZandt - Made using Gigobytes Character Sheet Creator below
https://www.dropbox.com/s/1xif5ij1v1x62lx/Chris%20-%20Kadan%20VanZandt%20-%20AToW%20Character%20Creator%20v7.xlsx?dl=0Major Kadan VanZandt - Just the finished printed PDF character page
https://www.dropbox.com/s/ql2tuj28njmr718/Chris%20-%20Kadan%20VanZandt%20-%20AToW%20Character%20Creator%20v7.pdf?dl=0Gigobytes Blank Character Sheet Creator
https://www.dropbox.com/s/pnsjupdg1fghdvv/AToW%20Character%20Creator%20v7.xlsx?dl=0Gigobytes WordDoc Instructions on using his Character Creator
https://www.dropbox.com/s/ae438javegkgovc/Character%20Creation%20Walkthrough.docx?dl=0Anyway, I Hope any or all of that info helps! Good gaming to you and your friends!
Cheers!
-CoreWatch