Have you attended any of the races at the track? If not, I would recommend you do and see what others are running.
As for the store owner stocking traxxas, did he say he wouldn't order other parts? You could always stock up on common broken stuff. For the T4, that would be to me the front a-arms as well as the carriers and steering knuckles. As for the rear of the vehicle, maybe 1 set of rear a-arms, and 1 bottom plate. Never really broke the rear carriers. Also, starting out, get the RPM front bumper large version.
As for speed and the like, I wouldn't worry too much about that as others have stated. Being steady is more important starting out than speed. Does you no good to have a car you can't control on the track.
As for vehicles to choose from, if you can get a brushless setup all ready to go right away, I don't see a problem with that. Just don't go insane when starting out.
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