I think all of your ideas are on track. Clean and scrape the seams and apply eternabond tape to them. On mine I also ran eternabond tape around my roof
vents. Dicore self leveling works good too, and around plumbing vents. After
cleaning the roof, if it still looks iffy I would consider coating the entire
roof with a product suitable for aluminum and going over the eternabond tape
and dicor. When I did mine I also removed the uneeded stuff like the luggage
rack and TV antenae. Once the roof is done then you can go on to the rest.
Brian