Hey syl i've had an idea of how to set up.
Build a big high hollow dirt tower basically the same size as a leg of the current dish make that into a set of templates in buildcraft.
In the new world we find the largest ocean then use a land mark to mark out 4 points 64 blocks appart, dig down in the sea bed to a set Y level that puts the towers at a decent hight abvoe surface, set the builders up so that they build a pillar at each point, we can feed them anything to build the legs of of, maybe stone brick or obsidian or something.
then on top of the pillars we build a huge surface (maybe square instead of round) and we set that up with stores machine shop etc basicaly it acts like the hutdoes now it's just a starting point.
in the middle we can build a glass tube down to the sea bed and start seting up a mine/quarry and the udner sea stuff.
i thinking if we used a qide diameter glass tube we could later install an elevator with chests on it using frames to access the underwater part.
now what I'm thinking is to raise the sea level in a huge circle (or straighter sections loaded into builders via a template and using natural features like mountains to help, ill have to seal up many caves too) we build a damn, say 20-30 blocks tall nice and ornate) then around the dam in towers we cans et up redstone pumps reaching it no oceans on the other side of the dam they'll pump source blocks i nand slowy fill up the damn so we have a ncei deap ocean to build in.
what i'm thinking that might be really coo lfrom this is the suraface we build onf irst will grow naturally liek the hut does as we need more stuff, (pump statiosn sticking off, energy generators, storage etc) to build the damn.
but the cool thing will be as the water rises parts of it will become submerged, I thoguht it wouldbe cool if we removed the chests/valuable machines but just let it take over the rooms (certain things like power gen or really usefull machiens maybe just water proofed) so as we build the surface based stuff it'll be a cool feature the old sunken ruins below the city