Were you ever able to get his "gimp" formally diagnosed? And is there a treatment plan in place?
If not, that would be my first step before really considering him as an option.
As someone who owns a horse with pre-exisiting "severe" medical issues (that went undiagnosed initially because I thought it would be "fine"), in the long run, getting a diagnoses+treatment plan now and possibly having to pass him up is going to hurt a whole HECK of a lot less now than it'll hurt in a few years when/if you discover (like I did) that what you had been doing actually harmed this horse you adore because you didn't know the protocol for what you were dealing with.
I know you adore this horse, and he deserves that, but I question whether he's the right guy for someone who wants to do more than just have a pasture pet. Nothing wrong with a pasture pet, my Lacey is a pasture pet right now, but it's important to have reasonable expectations and I'm not sure he'll hold up well/comfortably for anything more than pasture pet-ing it.
Of course, maybe it's something that's easily solved. That would be great and something that would be good to know!
I don't think he has terrible conformation. He does seem to have really high withers but some of that seems to be photo angle. His topline is also weak but that's a matter of work/muscle, I think. Otherwise he looks like a sturdy guy!
I can see why you love him, he has a really intelligent, kind, expression. I'm a sucker for grays and that last picture, well, there's a face you don't say "no" to!!