CS, I'm going to disagree in a couple areas. Because you actually being TOO NICE here.
1. That is WAY to many Mechs for Militia.
2. Field Guns are actually a new concept IIRC, the Assault Guards was just getting them IIRC, & wouldn't be nearly that common.
3. A Foot Infantry regiment is IIRC supported by a single platoon of Towed Thumpers.
4. Much specialty ammo is actually very advanced & not at all common at the Militia level.
Of all that you listed, I would say Flak, Smoke, Thunder, & Inferno are the only contenders for Militia.
I'd probably set it up as follows.
"Typical Militia Brigade"
1st Regiment
1x Foot-Green-Regiment
1x TowedThumper-Green-Platoon
1x LitTank-Reg-Platoon
2nd Regiment
1x Foot-Regular-Battalion
1x Motorized-Regular-Battalion
1x APC-Green-Battalion
1x TowedThumper-Green-Platoon
1x MedTank-Regular-Platoon
3rd Regiment
1x Motorized-Regular-Battalion
1x LitTank-Green-Battalion
1x MedTank-Regular-Battalion
1x TowedThumper-Regular-Platoon
1x LtMech-Green-Lance
Total = 9 Bat + 2 Co
4 Bat Foot Inf (3Grn, 1Reg)
2 Bat Motor Inf (2Reg)
1 Bat APC (Grn)
1 Bat LitTank (Grn) + 1 Plt (Reg)
1 Bat MedTank (Reg) + 1 Plt (Reg)
3 Plt Towed Thump (2Grn, 1Reg)
1 Lt Mech Lance (Grn)
difference between "Dirtbag" and "Scumbag" militia here, Hellraiser. Dirtbag militia is supposed to provide your better-equipped players with a challenging fight.
Scumbag militias are there to be stormtrooper mooks for heroic PC's to burn through like popcorn in a march to victory.
Secondly, is a tendency IRL for national guardsmen to get better ammo before they get better guns-when the M-16A2 was adopted, it was adopted with a new ammunition round. A lot of units got the new rounds before they got the new rifles, esp. thanks to Operation Desert Shield/Storm.
Field guns were part of the canon before they were moved from what used to be "Level 3 rules" (Maxtech) to standard play. Like rockets (as Colt pointed out), they're a logical thing for low-priority forces in bad areas to have, since they're relatively cheap, (cheaper than a proper vehicle and assloads cheaper than a proper 'mech), provide good firepower on defense, and can be produced more rapidly than 'mechs, tanks, etc. etc.
I'll note that the exceptional corrections in Deadborder's post would apply-when I wrote this, it was based on the assumption of players without full access to all of the TRO's (thus focusing on the most common ones you might find at half-price books or another used bookseller).
"Field guns" could be difficult to have rules for if you don't have the right books NOW, but SRM infantry isn't, so that can be quite easily substituted (and is potentially far, far nastier.)
Teh basics of Dirtbagging, is to take the lowest tech you have available that you can still be effective with if you're creative-in the old days, it would be designing a "Rules level one" unit that can actually make a Clan player sweat if used correctly-the variant ammo choices I gave were the "Top" of the Dirtbag tree-basicaly 3060 to 3080's era Dirtbags, likely to face Battlesuits, omnimechs, Blakist techweenies and Clanner munchkins.
Hellraiser: scaling back for eras, your layout works in 3025, and it's a good one. Scaling forward, probably see fewer 'mech types total and might see no 'mechs at all, but higher tech tanks or limited suit use (Dark Age).
the key point of Dirtbag militias, is the idea that the mooks might actually BE DANGEROUS, or (if done from the player's end) being peasant/middleclass/yeoman heroes up against corrupt nobles or slathering invading elites.
all in all though, "Dirtbag Militias" are intended to be something;
Effective.
As a GM, you trot out the Dirtbag militias when your players get munchkin-arrogant and need a lesson, or when your players are craving a 'decent fight' but aren't up to facing a Manei-Domini Level III in Experimental tech machines, or aren't up to the level where tehy can square off with Clan Regulars in 3050.
as a Player, running a unit that's based on Dirtbag principles is about using cleverness and old gear to beat what better units and men than you have failed to defeat, or it's about heroically holding a line against technically superior foes. This is WHY it gets the slack.
again, adjustments by era or house or situation are reasonable. A FWL dirtbag unit isn't necessarily going to look like a FedSuns Dirtbag unit, neither of them will look like what a Cappellan, Taurian, Canopian, Kurita, or Lyran Dirtbag unit looks like-but there are common elements to all of those that make them 'Dirtbag' instead of 'Scumbag' militias.
the most telling element, of course, is that the most advanced thing they're likely to be running, is the ammo in the hoppers. everything else is a combination of old, common, and cheap (relatively cheap).
but a few of the basics DO apply:
Dirtbags don't deploy large formations of 'mechs-a proper Dirtbag formation has a few, if they're well-treated, older 'mechs or lower-tech 'mechs, the main thrust of their combat power is conventional arms used intelligently, and 'mechs are basically in a role similar to horsed officers in world war one-they're there, but few in number and only a small proportion of the forces arrayed.
Dirtbags use cheap force-multipliers (such as low-end artillery) because they don't have large numbers of 'mechs, aren't likely to be leaving their world, and towed arty is decidedly less effective for the kind of offense that most of the major powers and Merc units in BT base their grand strategies on...that said, they aren't likely to have BIG guns (Sniper, Long Tom) because those DO have a use in offensive operations or defense of major cities.
Dirtbag militias need to be coherently laid out. A random-stuff miliz isn't Dirtbag (or scumbag), they're just ineffective. lots of commons that share design history or parts, have similar weapons systems, etc. etc.-the kind of thing you can build strategy or tactics around, fits the Dirtbag pattern-remember, these are supposed to be effective, but not overpowering to the level of a House Regulars outfit from the same era. For a GM that means giving the players a chance to 'figure out' their achilles heel or weakness, or to figure out how to negate their one or two advantages, but in a way that's relatively fair and open. (otherwise the mission becomes an interminable grind for the players.)
my own Dirtbag configurations were the basis of a lot of the stories I've done in the fan-fiction. they're a little bit difficult to use, and there's a lot of book-keeping to do with them, but simplicities I found included being able to copy off several identical sheets and using number designations to help keep track of things like shots fired (Important with ammo based forces), damage tracking, and 'morale checks' set into the scenario rules (Usually forced withdrawal.)
I've tried random-rolled forces and found them to be even MORE of a bookkeeping nightmare-often extending turns into hours that should have been resolved in minutes or even seconds. *(this got, if anything, WORSE with TW's update to how vees take damage.)
Now, I do confess to using some house rules;because they work OH so much better when I'm GM'ing a group of players...
1. Initiative: it's called "Front Load the Initiative for asymmetrical numbers of units!" win or lose, the larger force moves more units first, and fewer units LAST. this is almost polar opposite of how it works in the book, and it makes turns go much faster, and negates some of the raw advantages of having more units on the board, thus side-stepping the problem that they were trying to solve in BV2.0 with FSM.
2. When Dirtbags are on the menu, GM or Player, forced withdrawal is a must-otherwise the game bogs down into a month of sundays to resolve one, minor, battle. Depending on where the Dirtbags are, and who they're facing, the base rate is 50% of combat effectives out of action, and the Dirtbags HAVE TO withdraw/concede.
Depending on Era/location:
3rd Succession War:
Davion: 50%
Kurita: 65%
Steiner: 25% (*player controlled 50%)
Marik: 50%
Liao: 75% (Hopeless Battle Syndrome, PC controlled 80%)
4th Succession War:
Cappy: 25% (Player controlled 50%)-reflects lack of serious resistance in the backstory and fiction.
Davion: 50% (House Davion was a baseline for so long for the game, plus they didn't have to defend much)
Steiner: 25% (Social General syndrome)
FWL: 50% (Player controlled 55%)
Kurita: 60% (Player controlled 75%-reflects how the Kuritans actually fought in the fiction and background)
3039:
Davion: 50% (baseline, Pc controlled 75%)
Steiner: 50% (PC controlled 50%)
Kurita: 60% (PC 80%)
Cappie: 80% (Romano), 60% (that other Liao that married the spy).
FWL: 50%
3050's (Clan invasion era)
Rassalhague: 65% to 80% losses in most situations.
House Kurita : 45% to 80%
Steiner-Davion: 50% to 75%
3060's (Steiner-Davion civil war, Xin Sheng! era)
Cappellan: 70% flat rate (Player controlled 75%)
Steiner: 35% to 75% depending on location.
Davion: 25% to 65% (the Davion side was, for most of it, on the offensive. where they were defending, against Xin Sheng! they tended to lose in the fiction-and not boldly or heroically.)
FWL: 25% (player controlled 50%)
3070's (Jihaaad):
Everyone has a flat rate of 50%, adjust up or down depending on your interpretation of national pride. (Player controlled 75%)
3080s
Everyone has a flat 25% (player controlled gets 50%)
32nd century (Darkage)
haven't messed with this much, haven't put much thought into it. good basic loss rate to force withdrawal is 25% of combat power (that is, 'mechs and tanks) or 50% of conventional infantry forces.
Yes, I left out the Taurians, Canopians, etc. etc. in the Periphery-mostly because those 'houses' main fighting forces mostly conform to "Dirtbag Militia" standards already, Pirates don't have 'em and Clanners don't need them.
