For his foot wounds, you can use any antiseptic you have on hand. Anything to prevent bacteria from forming on the wound. Vetericyn is unique in that it promotes new tissue growth. It's a wound treatment I highly recommend for every chicken first aid kit.
I suspect he may be having some trouble with a clogged gizzard. The treatment I suggest is a molasses flush. It stimulates him to poop and will soften the gizzard contents to make it easier for him to poop. But it could be diarrhea, so prepare for a mess.
The recipe is one-fourth cup warm water with one teaspoon molasses stirred in. He needs to drink it all in order for it to clean him out.
You're on your way to getting this guy ship-shape again. Don't feel badly. You're doing the right thing. By the way, does he have a name? We tend to become emotionally invested in these little patients here. You and I are not the only ones rooting for him.