This is a mod which I think would be very fun. Unfortunately, I have next to no scripting skills, so I leave it to anyone kind enough to consider this idea. I would help in any other way I can.
Basic Concept: Essentially ARMA 3's scouting mixed with CS' money system.
1. Player is a guerrilla fighter who must perform missions (eg: simple ARMA 3 scouting missions)
2. Missions are given from home camps.
3. Completing missions and killing enemies earns player money.
4. Money can be used to buy weapons / gear from home camps (RHS weapons mod has plenty).
5. Player can advance in level and unlock better guns.
eg: LVL 1 player can buy SMGs, pistols, the M590A1 shotgun, etc.
Higher levels gain access to rifles, red dots, launchers and scopes.
6. Accomplishing missions (or perhaps killing enemies?) unlocks new levels.
7. Enemies are scaled to player level to allow them to use low tier weapons.
eg: LVL 1 enemies have no armored clothing, NVGs and carry low cal weapons.
8. Player must accomplish objectives solo - no friendly AI to manage.