1. Maybe, not as good as the SHs because he doesn't have what makes Luffy special. He would still have some good crewmates but not as good as the current SHs imo.
2. It really depends, if they role were switched, and if Luffy was ok with being a subordinate, he might be able to.
3. If all the plot armor that Luffy has goes to Zoro, definitely.