I have never replaced a roof on an RV so do not claim to be an expert. However, most RV's have the outside edge of the roof rolled over the top edged of the side walls to help prevent water from draining inside the side walls if the lap seal begins to fail. Don't know about the width of your RV, but standard width today of 8', so a 4'X8' Sheet would not allow any material to roll over the side wall. Otherwise, I think you are on the right track.
Not sure about sealer between the panels, but I would check on using 100% Silicone between them unless someone else knows better. As for the outside seams, I would highly suggest Eternabond tape for all of the outside seams and to cover the rivet heads or you could use self leveling lap sealant like the manufacturers do, but it will eventually dry out and crack like it does on new RV's. Good luck!!
Rick and Janice Binns
2006 MS 32TK3, Mor/Ryde Pin Box and I.S., Auto Level-Up
2012 Ford F450 6.7 L Diesel, air bags and 25K Reese Signature hitch (factory installed)