I'm not really sure how well the rpm thing would work, it'd be a tricky thing to do at a risk of killing your gauge. I'm not typically a fan of red in an interior, it was nixed in the early 90's for good reason, it's tough to keep clean. you want to keep high traffic parts dark as possible to not show dirt/spills/wear. ie floor, seats, things you touch. if you want to do red keep it a dark burgundy and only an accent, not vast swaths of it. You want to also keep in mind that if you just pull everything yo ucan and paint it people in the know will realize that, never good. I'd go with mainly black and a deep red trim, maybe a couple pieces of the dash and a vinyl/leather door trim to tie them in along w matching hilites in the seats