LOL. It is hard, and seeing as how it's your first horse you want to do it right.
Most horses I've worked with have all had their quirks though. Riley has horrible feet, Maple was prone to skin fungus', Sonny popped splints like there was no tomorrow, he's cannons were covered in lumps, yet he never went lame.
I find all horses have their quirks, it's which quirks you can live with.
Now, soundness should be non-negotiable. But something like weight or a bad coat is manageable, maybe to you.
Your headed on the right path though
You know to get a vet to check the horse before you buy and that's half the battle.
On the other hand, (of course LOL) At least half of the schoolies I've come into contact with couldn't pass a vet check. Whether it be feet, random lameness or stiff hocks. But they were generally healthy and did the job without being in pain, even though they could never pass a vet check.
Horses are complicated! LOL, As I'm sure you've discovered. Take your time. Speak with both of your instructors to see if they can keep an eye out for you