This, with some Game of Thrones politics.
The first thing I would do is get a popular, talented A+++ level artist, who could do some amazingly detailed, lush, underwater scenes and was interested in creating a definitive version of Atlantis and several undersea civilizations. Also who draws a pretty Namor.
Depending on the artist's speed, I might write fewer pages of the main story to give them more time, and have short back ups of Tales of Atlantis, to clear up that mess.
I would try to organically incorporate some other MU characters into the storylines. Off the top of my head, Dr. Strange, Emma Frost, Triton (revive him if he's dead) / Inhumans, FF, Doctor Doom, Jim Hammond... maybe some Eternals.
First Issue: Establish some governing body / advisors (Vashti and could include the cousins) who finally get Namor to agree to a marriage -- if they can find an agreed upon candidate. Short introduction to the other undersea cities and major houses / nobles of Atlantis, and perhaps potential wives. Establish Namor is working with Abira and perhaps the priesthood, and maybe even Dr. Strange, to find a way to protect Atlantis via magical means. Issue ends with an attack on a visiting foreign delegation by the Faceless Ones led by ...
I'm not sure how it breaks down by arcs, but the first issue would introduce the three main plotlines I'd deal with, while hopefully reinstating or expanding on the world building and cast of the Namor's world. I'd dig out all the introduced artifacts and perhaps introduce a few more from mythology or history, and used them. While there would be political threats like Attuma's barbarians and other undersea cities, the underlying threat would be something more magical and Lovecraftian.