Your melee/pistol/shotgun players are going to get obliterated. You'll have a hard time finding those who want to go and play with a foam sword and a pistol while their opponents use AEGs. Personally I would do the following:
NCR Troops:
-Weapon Type: AEG/GBBR, no special weapons( DMR, Bolties, Support weapons, launchers, etc)
-Restrictions: Semi-Auto Only, 3 Mid caps, No Optics, No Sidearm
-Med Supplies: None
Doctors (Medics): (2-5 Players)
-Weapon Type: Pistol or SMG
-Restrictions: Semi-Only, 2 mags
-Med Supplies: 5 Stimpacks, 2 Med Kits(I'll cover the difference later on)
Rangers: (5-10 players)
-Weapon Type: Any
-Restrictions: 6 mids/one box mag/ 2 mags(sniper rifles)
-Med Supplies: 1 Stimpack
Caesar's Legion Troops
-Weapon Type: AEG/GBBR, no special weapons( DMR, Bolties, Support weapons, launchers, etc)
-Restrictions: Semi-Only, 2 midcaps, no optics, No Sidearm
-Med Supplies: 1 Herb Kit
Prime Legionaries Type 1(Effectively Squad Leaders, give each one command of 5-10 Troops)
-Weapon Type: AEG/GBBR +Launchers if desired (No support weapons)
-Restrictions: 5 mids+ 3 shells(if used), No Sidearm, No Optics, Semi-Only
-Med Supplies: 3 Herb Kits
Prime Legionaries Type 2
-Weapon Type: DMR/Bolt Action + sidearm
-Restrictions: Semi-Only, 2 Mags/3 mids
-Med Supplies: 1 Herb Kit/ 1 Med Kit(their choice)
Centurions: (Only allow 2-5 of these total)
-Weapon Type: Any
-Restrictions: 10 mids, 2 box mags, 6 bolty mags
-Med Supplies: None
__________________________
Raiders: (Have maybe 1 or 2 small groups in play but don't have too many)
-Weapon Type: Any
-Restrictions: 4 mids, Semi-Only(excepting one player per group) and no optics
-Med Supplies: None
Brotherhood of Steel: 5-8 Players max
-Weapon Type: Must have either a DMR/Bolt, Support Weapon, or AEG/GBBR with a launcher attached. No basic weapons allowed.
-Restrictions: 8 mids/2 box mags/ 5 sniper mags
-Med Supplies: 2 Stimpacks each (1 player gets 1 Med Kit as well)
Basically to make up for a small number they have weapon superiority and full-auto ability, along with stimpacks.
In terms of Balance, let's use 100 players for a round number. This is just a rough idea.
40 Legion
30 NCR
6 Brotherhood
12(2 groups of 6) Raiders
12 Role Players(to spice it up with the story and objectives)
Now the medic system. The coolest one I've played with is one where each player got a roll of paper "cards". Each one had a scenario(some with a tinge of humor, this can be tuned for fallout and allows for an extra touch of personality for the game) that required a certain heal scenario, and sometimes restrictions on the heal. If you got shot you pulled a card and either healed yourself or get healed by a medic(card requirements). With a similar system tuned for this game, you have stimpacks/herb kits able to get people back on their feet, or med kits which basically alleviate the problem. Examples:
Wound Type: Headshot
Result: Go Directly to Spawn, no bleedout.
Wound Type: Left Shoulder
Result: 1 Stimpack Required. May then return to play, but cannot use left arm until. Use of Med Kit results in no restriction.
Wound Type: Chest Wound
Result: 1 Med Kit within 5 mins or return to spawn. Stimpack may extend bleedout by 5 mins.
Wound Type: My Legs!
Result: 1 Stimpack: Healed but cannot walk, must crawl or be dragged. 1 Med Kit: Healed and may walk, but not run or jog.
If I can dig up the deck of cards in my gear I'll post a few, the above are just some ideas. It was fun defending a village but not being able to move besides crawling or dragging or tying to take a fortified position uphill without my right(dominate) arm/hand. Ask
Cam or
Kimchee (aka AMAZN AZN) both of them experienced this system as well.
Anyways, those are just some ideas I would use were I writing/hosting.