I've been debating whether to join in here or not, because I don't want to make you feel hurt or pressured, OP... But in the end, I'm not really seeing much to like about that stallion either. What would worry me is if the foal got his dam's bulk and, say, his dad's legs... with the conformation faults of the stallion, I'd be worried that the foal might have issues with the bulk that your mare seems to put on her foals. She's lovely, but a big, big mare, who looks to pass that on, and that means that conformation is doubly important. Especially when crossing with a quarter horse.
I really, really, REALLY like your mare, and I feel like you could find a better stallion for her. She is such a lovely, compact, sturdy looking horse, I think she could produce a fantastic foal that is lighter like you want but also very high quality... I guess, basically, what I'm trying to say is that I think that the stallion is just not up to par with her.
Of course, this is all just my opinion. Don't feel like I'm attacking you or forcing my thoughts onto you, in the end, it's your mare and your choice. But I honestly think that you could find another, better stallion for such a lovely mare who has just as nice a personality/ temperament and much better conformation... Even if the foal is just your trail horse and companion for the rest of its life, why not aim for as much quality as possible?
I don't want to sound rude with my opinion. These are just my thoughts, and I hope you don't mind my sharing them.