I've been using hoof armor this summer and am only using boots in front for long rides. 75% happy with it. If he didn't have wonky action on one leg that wears one side down when going faster than walk on roads I'd get away without boots.
Have you been riding and he's reacted to what you washed your saddle cloth in? Just a thought.
I wouldn't put anything on it, it looks like an allergic reaction and you don't want another reaction to what you put on it.
Definitely get the vet to test asap for Cushing's and EMS. If you find a metabolic cause you can treat it. It may be a good idea if you can find another yard that is set up for laminitis horses where they can be together in a bare area eating soaked hay.
Yes it sounds like what my friends and I did. Help out with the ponies on a Saturday in return for a free ride. We were a little older though, about 13 , and we didn't have to pay anything, and did a lot less work than your child, manly lead reining beginners on lessons and catching/tacking up/...
I think the big drop will come when mortgage rates start increasing with inflation and the people who have been reasonably comfortable will start having to fork out more each month. I remember the 80s when I was buying my house and the rate went up to 15% taking nearly all my wages.