[Taqwus]

R'lyeh, with good access to astral and some to water, with the protection of being underwater, has a better setup than most for clam-hoarding, so if Wish is a goal you can make an easier play for it than most.

I would personally not choose blood magic, as blood is rather hard to use underwater (cannot gather slaves, cannot cast any spells or rituals which require blood slaves); you can push for it later if you like on land using blood starspawns, sages, circle masters, Garnet Amazons etc but you won't be able to use it underwater.

If you want to fill in gaps, try Death, Air, Earth or Nature. Death will get you summons, including amphibious fodder (and R'lyeh will want fodder for those nasty Triton hordes) and magical versatility (spectres), Air gets you Storms (good for protecting your mindbLasters), Earth gets you hammers (good for clam hording) and statues, Nature gets you wine bags (good for hungry hungry illithids) and versatility (lamia queens). You have good Astral already and some Water, and you can't really use Blood or Fire all that well underwater.

If you want a bless effect, consider Water 9; extra-fast Greater Othernesses, Things that Should Not Be and Formless Spawn make rather frightening bulldozers.