As DesMOND))o0o0o0o0o0 stated,
VFC -> AR/PDW platforms
(Avalons are expensive IMO.. you can get a cheaper VFC and get a better FET installed for less)
LCT -> AK/G3 platforms
Mosfet goes a long way, simple 3034 fet will suffice, and let you run 11.1v without any issues, SHS 12:1 or 13:1 gears, SHS HT motor, and a SHS 14 teeth piston head is really all you need for great trigger response and budget friendly

.
(might as well go full shs though inside since you're paying a tech to open it up anyways! nozzle, tappet plate, etc.
AEG vs GBBR debate, best to have both in your collection.
GBB's while fun, do have a lot of down sides, mainly weight, ammo cap, and inconsistency per shot (less gas in mag, means less consistent funnel of bbs at your opponent). AEG's are always consistent, and will go where you want it to shoot 100% of the time, do not need to worry about your bb's dropping because your mag is running low on gas. Weather for GBBS are another factor
(colder it is, worse the performance), but for indoors it is very fun, I tend to shoot less and make sure my shots count, as 30-40 rounds vs 50-160 round midcaps.
AEGs while a lot easier, once done, all you need to do is load your mags, plug in a batter, and go. GBBS you need to worry about dropping your mags, leaky mags, cleaning it, lubing it, storing it properly, and a lot of other factors.
(which may be fun for you to tinker with) - in essence, GBB's are a lot more work, but if you have time to take care of them.
Both are about the same price once you factor in a fully done setup (new) GBB +Mags, AEG + internals + labour
(mags are cheap)
Both have their ups and downs, if you're only thinking of one gun for both indoor and outdoor, I would suggest you go AEG, also mentionable, at any given time, a well done AEG's will outgun/perform anything.