You won't fit the motor mount to the standard kit without modifying the upper deck, so if that ain't your thing stick to the STD mount, so long as you pre mount your motor onto the mount before attaching the upper deck, you won't have too much problem getting it all in.
I got the center pulley but changed to 19t to allow more slack in the belts as they are REALLY tight out of the box. Note this changes FDR also which affects your gearing calcs.
Shocks are worth getting too. IMO.