The best accessory that I can recommend is plenty of practice ammo.

This rifle can be anything from a .22 LR plinker to a .50 BMG longrange thunderbolt.

Don't try to make it all things at once - don't buy a Porsche 911 and hang a snow plow from it! If you want a CQB weapon then your focus is going to be different than if you want a tack driving 14 pound varmint rifle.

It sounds like you're interested in making a CQB carbine between a rail accessory that will hang three different devices off of it and the tactical light. Personnally I have a one rule - hang one thingie off the rifle at a time - I violate that with my CQB pre-ban carbine in that I have a red dot and iron sight hung off of it. With your A2 upper a forward "scout" mounted red dot makes sense.

In my uses I don't feel the need to hang a flashlight off the rifle. I have a remote control and IR sensing lighting system that illuminates areas of the house with hundreds of watts worth of light if I need it.

A muzzle brake allows for quicker follow-up shots.

Buy mags, ammo and a case. Go out and get used to the gun as it is...You might be very happy and not need anything else. But at least you will know for sure. It's better than dropping money on what is good for me aor someone else here, but not nesicarily what you need/want.