Have you decided on the model of gun you want i.e. AK, M4, P90, G36 etc. That's where I would start if I were you. You're fortunate to live in a city that has several stores with showrooms where you can fondle different types of guns to see which is most comfortable for you to operate. Consider battery compartments, mag release, fire selector, mag shape/availability and what pouches are available for those mags.
Sounds like you're leaning towards an M4. If I were starting fresh with the intent of playing mostly indoor CQB I would get a Krytac CRB. VFC would be my second choice, something with a 10.5" barrel would be best for CQB, while still being good for outdoor. I don't personally recommend G&P, they suffer from embarrassing issues like off spec rails, non functional dust covers, charging handles, and gear sets that are prone to breaking. They do look very good though.
GBBR's are generally not recommended to the beginner especially if you aren't good at tinkering with things. The benefit of a GBBR is the realism (recoil, operational bolt stops, real ammo caps), but that's where it ends. GBBR's require more maintenance and care, they have very expensive and heavy mags with low ammo capacities, are more expensive to operate and generally don't shoot as well as AEG's (queue but hurt GBBR owners).
Last edited by Kozzie; September 7th, 2015 at 15:19..