Sceadu upgrades.DTDS and third bearing support are must haves.
QuickUk ally fan is worthwhile too for the extra cooling, along with the NHP shorud and frame brace.
A decent set of 600mm blades - I use MS but some people experience flutter. I also use SAB carbons.
Beyond that there is nothing really necessary. Just "eye candy"
I have pretty much all the QuickUK upgrades on mine, but wouldn't say that they have particularly improved performance.
It is worth tightening up the control system - most of the play is source in the control arms on the washout block. The collets that run through the bearing are about 0.15mm too long and this introduces lateral movement which translates to slop.