This is from my own docs i made when looking at this:
Valid tile sizes for importing as World Composition from something like world machine
2017x2017 - for 4x4
2033x2033 - for 8x8 tiles
2041x2041 - for 16x16 tiles
single tile res:
8129 - for 8x8 tiles
16352 - for 16x16 tiles
This is the documentation you want:
I think you will have to just build a bunch of tests in what ever you are using to create the world and import it and figure what is best.
Let me also take a quick moment to discuss some of the other stuff too.
From testing i found that when your actor gets about 1.5km away from the origin you will start seeing issues, like socket locations in animations being wildly off and jittery. The only way around this is to shift your origin. - cool.
One thing to take into consideration when you shift your origin this affects everything you have to design your code around this, its pretty easy just keep it in mind every time you send a vector to the server and then back to a pawn, there is a small translation you need to do on each end.
Materials are another one, that doesn’t get mentioned much, if you use absolute world position for things in materials, this will change when the origin shifts. So you want to reduce the use of any absolute world position calls in your materials, a lot of the time you can replace these with a location relative to the object (so it wont shift), or you need to find a solution to pump an offset into those materials every time you shift the origin.
You have quiet the journey ahead, have fun! 