Since there are a fuckton of Divine Domains in D&D, best to pick the domains you want specifically and make gods for them (for mechanical ease at least)
i'd probably go for gods having a large amount of domains instead of having a large amount of gods, i do agree with
@Goopy that keeping the god count kinda low would help with the feeling of hopelessness and that this world is severely lacking in its divinities
any other domain can be justified with "it's a niche sect of a particular god's worship"
Blind God I'd imagine would be both Trickery and Twilight domain, Moon God also Twilight domain, Sea God could effectively be the Blind God or if you want to go more Lovecraftian then the 'Sea God' could potentially not even be a God at all, but something like an Elder Evil or a Star Spawn Emissary that's so powerful that people revere it as a God; could potentially be Nature domain, or Tempest if you want them to be a storm-producer. Fire God would be a little confusing with the death of the Sun God, so rather than they be a Fire God would probably work better as a Forge God (as there's the Forge Domain) or possibly a War God (both Forge and War Domain) who makes use of the darkness to grow in strength at the perpetual ongoing wars for things like resources.
a lot of those domains sound reasonable, though i don't want to merge the blind god and sea god, the doctrines i have for them are pretty different and the vibes they're going for kinda clash
To make the darkness more scary, having a parallel 'god' that is the darkness could be interesting, giving them the Death & Grave Domains. Allows for a unique approach with necromancy where rather than a focus on zombies and skeletons, Shadows and other less-Luminant beings are the primary undead that populate the spaces
i'd spoken to a few folks about this before, i think i'd rather there not be a Darkness god, if only because he'd just be by far the most powerful one and would invalidate much of the worship of the others. maybe the things that lurk in the dark worship some kind of entity, but it's nothing a mortal man can acknowledge
How do you plan to re-balance races with this in mind? Some races and sub races (especially the subterranean races such as Drow, Svirfneblin etc) will become significantly nerfed this way
for custom settings like this, including my previous custom settings i'd made, i tend to make my own depictions of the fantasy races with their own lore. usually 8 relevant races that are core to the world's lore, and then if someone really wants to play a race that doesn't fit within that I'll see if i can add them to the lore (with mechanical changes etc)
like in this world i doubt there'd as much subterranean life, if only because the underground is pitch-black and full of all manner of monsters
i definitely think some cultures would still try it, to varying amounts of success