ARs are like legos and if you think you might build more than one there is nothing wrong with buying some piece of gear and trying it out, and having it go in a drawer if it doesn't work on this particular rifle... it might work on the next. I've got a drawer full of all kinds of stuff that falls into that category, and it seems I dive in there for one part or another on just about any rifle I get these days.
Personally I like relatively close in VFG on carbines. If I had a rifle with a long rail/tube and/or wanted to use it for 3gun I might take a look at the FAG. I put ladder sections on the top rail and exposed small portions of the side rails, but prefer a more full panel of some sort for the majority of the bottom and side rails since I think they are more comfortable and protect your hand from heat better. I think mine are Magpul XT's, they are light and have a nice texture.
I have a mix of all kinds of magazines; PMAGs, USGI, 20s, and 30's. 20's are definitely nicer off the bench and shorten the profile of the rifle in general when that is desired (for storage with mag inserted, etc).
Looks like you are off to a good start.