You're not going to be great at tap the minute you try it, it'll take a year to get the basic technique down before you can move on to big impressive moves.
You'll probably want american or broadway tap, youtube the different styles and pick the one you like best. If there is a basic beginner 'tap class' sign up for that first and stick with it for a few years until you're strong enough to branch into specific styles.
Tap dancing isn't hard to learn, but it is hard to do properly. The moves themselves are simple when broken down into baby steps. The same little steps form all tap moves. The thing that makes tap so hard is that it is FAST. When tap gets fast it is harder to make all your sounds. A good tap dancer gets crisp, clean sounds while dancing fast. It looks effortless. In your first year or so of tap training you'll be going slowly.
Energetic and good balance will certainly help you. Flexibility isn't necessary for tap, and actually most ballerinas are rather tall (5'7ish at least).
Bring a pen and notebook to class and write down the moves you learn. That way you can go home and find them on the internet. If you're struggling with a shuffle ball change or some other move you can youtube a ''how to'' video and learn it at home. It's very helpful.
Another thing....if you can't say it with your mouth then you can't do it with your feet. Say the moves out loud as you do them. When I tap I'm going 'stop brush hop hop flap step stomp, leap shuffle step flap step stomp, grab off grab off' in my head. It sounds like nonsense when you write it out like that, but it's the only way you'll ever grasp the idea of what you're doing. Your feet won't dance on their own, you need to use your brain.
Make sure your tap shoes fit properly, don't buy them five sizes too big so you can grow into them. You'll flop around like you're in flippers and you'll have a hard time getting your sounds.
I'd recommend a Bloch or Angelo Luzio shoe for your first tap.