I am Captain 1st class and played since CBT till now (9 month break) and I have,
12 pointman weapon excluding MP5A3 including 3 euro capsule gun
18 rifleman weapon excluding G3A3 including 6 euro capsule gun 1 Gcoin capsule gun
8 sniper weapon excluding M24 including 2 euro capsule gun
1 pistol which is the MK23
Only have bought 300 Gcoins total, 149G on Noel SAKO and 149G on Noel Kriss.
There is no trick, it's just you have to manage yourself and be patience:
1) If you are interested in euro capsule gun, do the 20BP everyday, eventually you will have 500BP, then you take a moment to scan your desired weapon, if they are below 120/200, start camping, if not go out and keep playing, wait until you see 5x/100 then buy 10 for high demand guns like desmodus, or wait until 4x/100 for low demand gun.
2) Do not waste time to farm 3 box and waste them on individual capsule, you may get lucky one time, but generally individual capsule is not a smart choice, regular cap is.
3) If you want a better life in AVA, you have to farm 3 box frequently, but with Aeria coming to AVA, and I feel like pay 2 win era is here soon, so it's up to you whether you want to farm or not. The easiest way to own in this game is by buying Gcoins no doubt, but you will not feel rewarding from what you buy.
4) Do not buy anything in the shop besides permanent guns, for me I still have AA-07 armor in my inventory and I use it while I play annihilation, it helps a lot and that was it.
5) Do research regarding every weapon in depth before buying any permanent weapon, and their mods, so you don't have to re-sell the weapon which is about 1/5 of the original price you paid.