Everything
@abraga said. I would get the blu-kote w/ the dauber, not the aerosol. It gets all over the place and was much more difficult to control. The dauber was much easier to use and get a good coating. It is going to stain his feathers.
I never found out what started the original problem. He did end up w/ a bloody tail again later, but I know it was from my pullets pecking at his tail that time.
I wouldn't separate him unless you see them pecking at his feathers. My amberlink pullets are very pecky. I actually keep my leghorn separated from them unless they're ranging b/c even though he's been healed for a while and his tail feathers have grown in, they keep going after his tail feathers, comb, and wattles.
I hope your guy heals quickly.