I have no access to my main computer due to lack of space in the house so I can't create the world for now or test these theories. So I'm just doing some research on my laptop and getting ready for the world design wise.

I don't know well enough about the docks/piers. Is it possible to just build one in the middle of an ocean?

I realize there might be routing issues with this though. Not only that I don't have any roads planned in this city. But I plan on leaving a bunch of space between most buildings so that there's enough room for boats to go rather than one way kind of deal. It's a strange idea but it's going to be fun and challenging if possible.
It's going to be a relatively small town but the map will be 2048x2048 so that I have enough space in case I need it. It will have almost all lot types except ones that wouldn't make sense. You know like, the Equestrian Center. Horses will definitely not work well here. ( Hopefully they don't ever spawn in the town either. )

Would this work? Or would the routing be pretty bad if I do this? I can just simply add bits of pieces of land to make it work but I'd rather try without. But if needed I will have to.
Also one other question, when I grid the world on paper how big are the lots to the 2048 map size? For example, how many pixels would a 64x64 lot would be on the map? What is the pixel ratio to lot sizes? Or is this not really known? Just a curious question. I can just make sure everything fits the map but it just would be easier to my OCD brain lol.

Sorry for so many questions but I've searched a ton and found nothing about any of them. :c
I've never made a world before, other than the test world I made to just get the hang of CAW. So this is my first true world. I'm hoping I can finish it too.
If I had my scanner I'd show my concepts here so you guys can see what I mean. I'm also gonna do some clothes for sims too, and stuff, but no scanner, it broke/lost the CD. :c

Doing all the research first is a good idea, because it can be a lot of things to think about. Sometimes it has to be tested though.

I haven't tested this myself, but I've heard other people wanted to make an underwater world and couldn't do it. They had tried different solutions and had different disasters happening to them apparently. For that reason I think you have to have something above the water.

About your plan to make lots on water with only a dock foundation on it. It could work, to my knowledge they don't need the access to ground, but it has to be tested. You need lots to build it on and the water depth should be the deepest caw will let you do.

Horses and other animals spawn on whatever land you have, but I think you could make your world into a city or something to prevent some of the wildlife you get on normal maps.

Roads are not needed, cars need them though, bikes need pathways. You have a very big map, do you plan on having boats going everywhere? That could work I guess.

I would leave pixels out of this. A world is devided into chunks, I think that's the spelling. My small map now has 4 of them. I haven't really looked at how many lots you can get in one chunk, but I would expect a bigger world to have more chunks. We also sometimes use the word grid for the grid you have on a lot when you build walls and other structures, and on ground. I found a discussion when I searched using these terms "how many lots on a chunk in caw".

Discussing: http://modthesims.info/t/455319

They have a few interesting ideas there, about max lot amount and perhaps if you do 2048/64 you will know how many lots of that size you can have. That will give you 32, that could be right. That will give you 32*32 = 96 lots on a map 2048. You have to make sure it's room between them, you can't just fill it all up.