JG, CA, G&G, TM, ICS... you will not go wrong. Wait for your age verification to go through before you make any final decisions as you are almost guaranteed to save money by buying used (but be wary of people who clearly ask too much for too little product).
Regarding sidearms, much of it boils down to personal preference. The "hi-cappa" pistols appear to have the largest aftermarket following and thus would be the logical suggestion. However, I don't like 1911-based or fictional sidearms (I'm a Glock fan) so I've been running with KSC/KJW and have had no problems at all. Both the ABS and metal versions are top notch and there is a plentiful supply of upgrade components available.
IN OMNIA PARATUS