So I read the whole thread and I think it looks more like Marek's than anything else. But if he were mine I would try to treat for the other stuff just in case.
Is taking him to a vet an option? There was an episode on one of those vet shows where someone brought in a limping rooster that recovered after antibiotic treatment.
If he were mine, I would go into full blown treatment mode and treat for worms, coccidiosis, bacterial infection, and vitamin and mineral deficiencies. I would also give start tubing fluids, then tube fluids and baby bird food.
He's a bird and needs lots of fluids! A small buff Orpington weighs about 8 pounds, a large one 10 pounds.
An 8 pound bird needs 6 ounces of water per day.
A 10 pound bird needs 8 ounces of water per day.
Dehydration and mineral deficiencies can look like Marek's too, so I suggest that you think about learning to tube.