OP, I’m sure the horse is lovely, knows his job well, and has taught you a lot during your yearlong lease. But you’re quite clear about two things: 1) you don’t show often, maybe once a year and 2) you’re an amateur rider contemplating the purchase of your first horse.
My advice is: Do not buy this horse. If you were uber wealthy and had plans to show in the big time, you might say to yourself, “Well, what the heck. He’s a nice horse and I’ll take the gamble that I can get one good show season out of him.” But that does not sound like you,
Second, you are indeed way over your head in evaluating this PPE finding. It takes years of experience and plenty of heartache to develop a reasonable set of guidelines for what is and is not an acceptable risk, given that any horse can injure itself or develop some unforeseen problem that can end its career.
Do listen to the people who are telling you there are all kinds of red flags here. You would be much better off with a sound but perhaps less fancy horse you can have fun with, given your modest ambitions. Of course, later, if your goals change, you can always “trade up” so to speak.