I certainly wouldn't pass him up
I don't see a long back, weak loin or long cannonbones at all. His legs look nice and clean, and the toeing out in the back is somewhat normal, since, when trotting fast, hind legs pass fronts by quite a bit.
Somewhere here on the forum is a weight calculation which is a bit more reasonable than the 20% rule.
Weight of horse + weight of rider+ tack : circumference of mid cannon bone : 2
If the result is 75 and under everything is fine. Above 75 up to 80 is still okay. Anything over 80 is bad.( measured in lbs and inches).
If you're dieting right now and get him trained so he will be in shape, I really don't see a problem. Easy to figure out what your weight goal should be.
I do see the kind eye too and he is quite a good looking fella.
I'd say go for it. Gives you motivation for your weight loss too. And, as you probably know, Standies are puppydogs once they have their own human, have a very good work ethic, can be even gaited and are easy keepers.
So, I'd say go see him, do the math, and give him a try