I've never owned a horse, but I know that feeling of nerves. You want that one to be "the one", and put internal pressure for them to like you and so on.
My suggestion is this. Be VERY honest about your abilities, doubts, and excitement. Bring someone with you. If you have any doubts, don't get him. There are lots of horses available, and you want to make sure you get a good fit/match FOR YOU. The perfect horse for you might be something completely different than you think, and the more you look at, the more you'll find out about what you want.
For instance, when I adopted my first retired racing greyhound, I thought I wanted a calm, female, small "couch potato". Each one I met was more interesting than the last, and I ended up with a big, goofy, white and brown male. He's a goof and I love him to death!!! I would NEVER in a million years have guessed that he's what I would end up with, but each dog I met was better than the last, until I KNEW that he was mine.
I suggest that you wait for that feeling of KNOWING that the horse is absolutely right for you.
Good luck!!! And remember, a great horse is out there for you, whether this guy is it or not.