-Good CHF barrel with a nice aluminum "railed" handguard - i like M-LOK
-Magpul flip-up sites
-Good ergonomic Magpul Stock
-Polish the trigger or get a 2-stage
-Optics will quadruple the initial price - aim point or MRO = 400-500
-Also can caliber convert to almost anything imaginable
-50 or so mags just incase
In all seriousness, enjoy! These things are as addictive as Glocks...and multiply similarly.