in his case, the health issues WLL take priority. You will need to handle him to get those soaks and treatments going. And cage cleanings! Clean the cage as often as you need too. Only paper towels and simple hides for now until the mites are gone. So don't worry as much on handling for the moment...but do keep it to a minimum. no handling outside of the soaks and applying the medication. His body condition overall looks pretty good, so I would wait at least a week to try feeding him. Get him healing before you try feeding him.
If he was eating small prey items before, don't try and feed him anything too large too quickly. You won't want him regurging on top of the other issues. If he's really fussy about food and is mostly healed? That will be when you go to the no handling mode to let him settle in and get less stress.
RE: wobble morphs, the spider gene can indeed be the cause of the wobble right now. Stress will make it worse. The downside is, parasites and infection can also make any snake wobble. Hopefully once he's settled in and healthy, it will be less noticeable. My 2 with spider won't noticeably wobble unless I really stress them out.
Champagne is the other gene that can cause wobble you may be thinking of. Cinnamon can cause kinking or duck billing on the face in the super form, but not known to cause wobble.
Re: size, it really just depends on the snake. Some males do stay more petite. My oldest male is a monster, larger than most females I've seen and weighs in at 2400 when he's not fasting. Another male I have is just a tad larger than yours looks at 3 years. BPs do tend to like smaller spaces sometimes so he may do well for life in a 20 gallon. You'll need to see how he reacts in a larger enclosure. If he seems stressed you can try adding more décor and hides in a larger enclosure, but that's when he's healthy and you know his habits and he's eating well.
One of my girls is a tub only snake (my older spider actually). She will perch up high in a striking pose and just strike at anything she sees moving. I can't keep her in a glass front enclosure. One will wander out and about and eat great in a glass front... another will only peek out of the hide when food day is coming. Each snake can have their own quirks.