i highly recommend Craigslist to new bikers. Get yourself measured and purchased a bike on craiglist that seems to fit the bill.
Seeing as you are riding on both road and trail its great thought you bought the hybrid and not a pure road bike yet. It sounds like your well on the right track!
As far as speed and things like that go it really depends on genetics and also what kind of shape your in. I have a bodybuilder type body and am in fantastic shape but im happy to average around 13 to 14 mph on a good day. Mountain biking and road biking are both fun on theyre own and if you decide you like the sport i highly recommend getting both a decent mountain bike AND road bike. mountain biking for the rush and road biking for the freedom.