I'm a college professor, and I TOTALLY agree with the people who suggested waiting until the winter break. You are going to find out that college is 100% different from high school, in many many many ways. PM me if you want more info on that. But give yourself the fall to get used to school, and then work your new buddy into the picture.
You might want to re-think the issue of Xrays on the PPE if you're planning on doing much jumping. My first horse (that's him in the userpic) is a retired show jumper and has some major thickening in the joints of his front legs, and possibly a little arthritis as well. I passed on the Xrays because when the vet said "don't jump this guy higher than 1 foot, unless you want to be feeding him bute" I took it seriously, and he's presently getting a second career in dressage. Something a little less hard on the legs. If I'd wanted to jump him, well, I probably wouldn't have bought *this* horse because he's just had a ton of wear and tear from jumping...but if I'd been looking at a horse for jumping, I would definitely have wanted more info about the state of his joints than could be got by a visual and physical exam.
What I did do - even though I was not at all concerned about the possibility of doping, because this guy had been my lesson horse for a couple months before I bought him, and if he was getting doped for the sale, it was happening on a daily basis before that - was to get the blood panel. This added a hundred bucks or so to the cost of the PPE, but it is well worth it! Not, as I said, because I was worried about doping, but because it would provide early warning signs of metabolic disorders, etc. - and in the event that there wasn't any of that - it provides a good set of baselines for him. Now, if he gets sick and the vet has to do a blood test, we know what his "normal" is and that will help us identify what is *not* "normal".
One other thing is that you should not be getting the horse's regular vet to do the PPE. There's a conflict of interest there. It's a good idea to get a vet that isn't familiar with the horse - that way, they are less likely to overlook something that might be of interest to you (which could happen if they know the horse, and they're already aware of Problem X and don't consider it to be a big deal, so they don't really think about it. This doesn't mean the vet is "bad" - it is a basic human information processing problem...they can't help it. That's why it's good to get a fresh set of eyes.) Also, when you go to check out the horse, look at it for any signs that it's been worked recently (sweat ripples, etc.).