I just want to point out that there are many other guns than AR-15 variants and, as much as you may see yourself with nothing else, before you buy you should at least have a feel of a few different assault rifles and an SMG or two. To see how the layout of the controls suit you and what it's like to reload I would suggest trying any old M4, or indeed the CM18 MOD1, an AK-47 or 74, a G36C or better a KV, an MP5 SD5/6 if poss or A4 for the classic style, an MP7, and a bullpup - an L85A2, FAMAS, TAR-21, or Chinese Type 97.
There are loads of things which will prove more useful for skirmishing than a pistol. Spare mags, something to carry them in, spare battery, kneepads, better boots &/or socks, alternative eyepro, gloves, BFG and pouch / pouch for MK5 pyros...