The floating could indicate internal problems. My Betta floated sideways when he had internal parasites. Aquarium salt wouldn't help this. That would be something you would treat with Epsom salt as its either an internal infection or something is wrong with his swim bladder. However, I would not mix aquarium salt and Epsom salt which is difficult when he has ich, fin damage and an internal problem. Epsom salt could be combined with medication, however.
Trying to treat all of these at the same time will be both difficult and also stressful to the fish, but at the same time, not treating it will probably result in death. Even if you do treat it, it may be too late for him.
Also, Epsom salt alone would not treat it if it were an internal parasite or bacterial infection. You could try a medication for ich and Epsom salt for the floating plus stress coat. It sounds like he's not in great shape and I would be prepared for the worse at this point.
Edit: I believe the Epsom salt might also help his fins slightly. Does he look even slightly bloated? My fish had very slight bloating with internal parasites.