+1 to canebrake's recommendation to shoot the snot out of the gun. I would say get your iron sights and then run the gun, and only after you discover a problem should you go looking for a solution. I don't advocate hanging anything on your rifle that does not solve a problem for you.
That said, I would recommend you get the longest railed free float forearm that your barrel length will support. This is because it will give you a longer sight radius making your rifle easier to shoot accurately and because I am an advocate for a support hold on the forearm that is as far forward as is comfortable. I feel this gives the shooter the best support in their rifle hold. You, of course, should make your decision on what is comfortable for you. The Daniel Defense OmegaX rail is designed to cover a low profile gas block, letting the rail extend out farther. I'm sure YHM, BCM, or others have quality rails with similar features in the price point you're looking for.
I would also recommend an ERGO Gapper. Its a couple of dollars, and fills a small space behind the trigger guard. The space wears on your knuckle and is annoying (at least to me). The space can also be filled by the Magpul replacement trigger guard.
For a fighting rifle I also think a white light and a sling are mandatory.
Good luck, and let us know which way you decide to go on your options.