I’ve always done it all at once. Lots of shoe polish as release agent. Lots of tape on everything else. Wrap the barrel in enough tape to keep it centered in the channel. Shove show wax into all holes you don’t want crap getting into.
Put it together where when it’s dry and just finger tight torque that it fits and functions nice as Simon said. Do this several time touching it as little as possible (it’s gonna have goo on it eventually, you want to make sure you can do it without making a mess and touching compound onto every other surface)
Then wet it with compound and redo.