Congrats on your first sail! speed633 has some excellent advice. Cats don't have much momentum, so as soon as you start to tack your speed falls off quickly. My biggest "aha!" moment was in the realization that you need to let the main out slightly after crossing the wind, to prevent it from turning the boat into a weather vane. The jib also helps to push your bows down/away from the wind, once the bows have crossed the wind. It also helps to keep your weight forward until just before you start the turn, so you're not dragging your sterns and slowing the boat down coming into the tack.
For a newbie, I'd say wind speeds of 8-12 mph are just perfect. 12-16 gets you out on the trapeze if you're a bit lighter, or at least hiking out. Over 16 the boat can be a handful, but that's also where it's the most fun! Under 8 is frustrating if there's a lot of chop on the water (d@mn power boats!
), and under 5 it's tough to keep the boat moving, particularly downwind (not enough pressure on the sails to keep them full).