From my experience, cars without tachs usually have the lowest base engine in them. That often means an engine that makes most of its power in the midband range with a rapid decline in power approaching maximum revs.
Everybody else gave good advice on shifting, so I'll throw in on the stereo: It's probably a proprietary plug for a factory CD changer. If they still make them, just get another casette adapter, or maybe a new HU.
Did the higherend Proteges have tacs? If so you might just be able to swap out the whole gauge cluster for one with a tac. The wiring and crap will probably already be there but you would have to ask somebody that knows proteges.
I don't suggest doing this often, but rev it high sometime as you are accelerating and see if you can find a fuel cutoff... That should help you identify how far away you are from redline when you are accelerating hard.