Thanks for the comments, and sorry this reply is so late!
Good news is I do have a great orthopedic vet who has been following PB since he was 7 weeks old. This vet didn't diagnose the HD, but has been following Po's ME case, and works in the same practice alongside the vet that did the hip radiographs. So if/when surgery becomes a necessity, I do have a doctor I trust.
I'm a full time student, and I make just enough to cover rent and pay for mine and my animals' necessities. If Polar were in pain or having mobility trouble, I'm sure I'd make a new plan, but for now I want to hold off on surgery until I am in a more financially secure place. Trust me, I had no plans to adopt a dog while in college because of this exact issue! My vet doesn't seem to think he needs surgery right now, and I trust her medical opinion... but I am definitely prepared to make some hard decisions if surgery becomes an immediate need!
We are pretty sure Polar has at least mostly grown into his ME, if not outgrown it completely, as he hasn't regurgitated anything in months. I'll be bringing him in for another barium study to get an idea on how/if his condition has changed probably in December, when he's a little over a year old. I worry, though, about about how it will effects his hips long term if it hasn't completely resolved.
Thank you for bringing up some ideas to think about. His vet wants him to keep active and moving as much as possible, so I will have to ask her about specific exercises she might recommend. She thought swimming would be good for him, but I am still too nervous about the ME to let him in the water. I'll have to talk to the ortho vet as well about what he thinks.
Thanks for the nice comments guys. Gotta say that I'm so thankful for all the other people who were involved with saving this poor pup because even with all his screw ups, I love my disaster dog.