I have 3 pmags and 1 stanag. just cuz the pmags can be bought in 3 packs for a lil cheaper than 1 at a time from hongkong.
as for the EVOII hop up tensioner as suggest above, they seem awesome! but are apparently sold out all over, unless you wanna buy the one that comes with the pistol barrel etc as they are interchangle able.
I also think the new lm4's. as in the ones being produced since the 'old' are all sold out lol have the hole drilled for the Bolt Catch Mod.
I highly recommend doing this mod. I waited a long time before doing it and the continual bolt releasing rounded my bolt and my bolt catch and now its VERY intermittent. The bolt catch mod is one of the best things you can do for the lm4 in almost every post ive seen or read.
Ive also got a RA-tech 6.01, and the npas installed. A cut down real steel A2 buffer so more recoil

haha
ill probably look into the maple leaf bucking and the steel arm because the standard hop is ok. but not great. the improvement is apparently extremely good!
if you wish to take off barrel nuts etc. They are often locktite'd or super glued..or welded.. haha not welded but it honestly felt like it. Some people have litteraly torn their guns inhalf trying to remove the barrel nut so have a torch and proper tools to melt the glue or lock tite to be safe!