I'm searching for a large empty world, that I can customize to contain lots from all of ther Sims 3 EPs. I'd also like the world to contain room for at least one houseboat and one divingspot, but those are not deal breakers.

I hope you can help me with this one!

Be careful what you wish for, you might get it.

In building worlds for the Sims 3, you have to be careful to limit the number of lots in a world This is especially true of residential lots. The default story progression tends to fill every lot with the maximum number of sims. The game starts to bog down as the number of sims increases. You do not want more than 200 sims in a world, and even that is too many. 50 residential lots at 8 sims each is 200 sims, and is a game which will quickly bog down.

Also, each lot may contain routing errors. These routing errors accumulate to the point sims get stuck and the game comes to a grinding halt.

Nothing is stopping you from creating flat world in CAW, adding all the lots you want. I could probably be done in a couple of days. I just would not recommend it.

I recommend most of the empties pre-made worlds, so that you can rearrange them in the way you want. You can find them on this site by searching.