Jumping is a lot of fun, but you definitely want a trainer working with you, especially if you have never done it before. It's not my favorite discipline (it was when I was a kid, though!) but it can be quite a rush!
As for conformation, there are certainly things to keep in mind and your trainer can help with your horse's specifics. My horse is half app--very stocky and big and really short legs. Not exactly a great jumping mount but she LOVES it, so we do it from time to time. Her brother was similarly built, I hear, but he was a champion jumper so you just never know!