i think u hafta set a price range first bud.. i dont think a used TSX and a IS300 are in the same ball park....
never been in a IS so cant help ya there. but do get a 06 TSX if u consider it.
dont doubt ur install skills but OEM navi and bluetooth > aftermarket
ever think of the civic si sedan? just a thought to save some $$. its got the power, navi, and itts pretty comfortable...