I have a 08 RXTX and so far I have waiting to be installed Riva waterbox, riva powerfilter, oil catch can and R&D intake grate. on planed list for next is riva intake manifold upgrade kit, RE's OPAS block offs, intercooler water strainer.
First mod you could do wont cost you almost anything but will help is to fill the ride plate holes.
also for a air filter some go with kanaflex hose and universal filter.
I think I have seen some mod their intake grate too to some succes.
you dont have to get the waterbox as I did, riva makes free flowing exhaust tubes, one is used to remove the resonator and uses the stock exhuast exit location. other is thru hull pipe and you will need to remove the OPAS to install it.
impeller or pump wedge is not needed for first mods, stock impeller is fine for time being.
OPAS removal is kinda needed at some point cause at high speeds it causes instability.
you can get a charger at some point too for more boost.
I like this site to order from
http://pwcmuscle.com