There are some good design ideas on this thread, but I don’t see a consensus of the sea village size - A lot of the power supplies and usage not be known until the village is up and running, and needs assessed.
I currently have a 24 volt PV on my house (3 - 165 watt panels, 4 - 6 volt batteries wired in series for 24 volt storage) that I use to run a freezer in the basement. Long Winter days requires that plug into a battery charger when I have no sun for more than a couple of days. Most of the time I produce more power than I can use, which ends up getting wasted. I checked into a grid tired inverter to try and sell power back but it cost more than the amount I would get back. I was excited to see the current issue of Home Power Magazine with a thorough article on micro-inverters which might make it affordable to good connect (but I also didn’t need the complications of code requirements of interconnection). Managing community power with one’s home power can be complicated, depending on how communal one would want to be. A bigger community might have some large moment of power requirements if they intend to do some manufacturing - welders and such. (Running away from a storm, maybe).
I would love to experiment with using cool seawater for space cooling. I was a solar hot water heating contractor for a while and know something about heat exchangers, radiant floors, and backup systems.
From experience, I know that DC pumps (motors) use less power for a certain load than AC.
A heatpump will deliver about 3 times more BTUs per watt than resistance heaters.
Sewage is going to have to be processed - methane production is a no brainier - maybe it can be coupled with hydrogen gas from natural power systems (solar, wind, and wave) food production is primary, so yes to fertilizer. I would like to know more about a gigantic seawater flow-battery that can also be used as ballast weight.
So what is the minimum size of village would it take to support a small medical facility?
I vote for more DC power systems than AC, and I would plan for times when the power is low - and try to not use fossil fuels, if at all possible.