Wow! If that's just the first room, the ruin's going to be huge! I hope you have enough story to fill the whole place!
It's really not that big, the overview is kinda deceptive. It's actually only two daedric rooms, some tunnels, and two side caverns. Most of it is underwater though, so I'm sure it'll feel big for a player suffocating
. Anyway, about the story, are we still going with your original design concept? And is it still part of the main quest for the island? I can write up a new story for the place if needed, but I need to know what level of importance this ruin's at right now.