Any or all of these moves would be fine by me. I would like to see a gear 4th/overdrive. I imagine Luffy using gear 2nd but going into overdrive with some of his limbs engulfed in flames. This would definitely make him Admiral level.
If Luffy did intake the Mera Mera, I wouldn't want him to be intangible like other Logia...not that it would matter. I think Japanese fans would go ape shit of Luffy having a second power. American fans...not so much.