Flatline= junk, neat junk, but junk.
Double triger, no point realy unless thats your thing..
RT- Not a bad choice, had one on mine before I sold it. Great for short bursts. Most people misconceive RT as Full auto, its not, well it sort of is but 8 out of 10 people cant go FA with it until they get the feel of it down.
Regulator, A feamle Stab should work nice, also get an "rva" for the gun (to adjust dwell)
PArts kit- get the full one, think 888paintball sells them.
Oh yeah, dont remove the "tombstone" unless you need to, the valve has a tendency to fall apart.