Is there a way to merge cells in the CK? The player home mod I'm working on is currently made up of at least 4 cells and it's really annoying working with some things across cells.
If the answer to that is no, is there a way to determine the size of a cell when creating from scratch or is that baked in?
Technically yes :
1) Double click on the cell you want to merge other cells into, so it load in the render window
2) Select one of the cell you want to merge in the previous one in the cell list with a single click (so the previous one is still the one in the render view)
3) Use Shift+Click to select all the content of the cell you want to move to the new one (from the list in the right pane of the cell view window)
4) Do a massive drag n drop from the list to the render window.
But you'll probably need a few try before actually having the two cells merged properly, so don't forget to save before doing this ^^
Be aware that drag n dropped stuffs keep their relative position, but the origin is the top of your cursor. Be sure to drop in a place where there is a "little something" (just add a tile of floor where you want to move the stuff), or the Z position will be super-messed up ^^
Also : don't drag n drop the navmesh if there is any, rebuild it once you're done merging/editing. And check in game, i don't know what's in the cells you want to merge, but if there is a lot of stuff linked to each other (like activator and so on), stuffs might end up broken.
And finally, you'll have to switch every loading doors to simple doors. And perform a quick check in xEdit in case there is any record that's kept from the former cell in the dat of the placed objects you added (stuffs like location, owner, and so on...), I'm not sure how this is getting copied when you use the trick described above. If you have massive changes, throwing in a small xEdit script to fix it all should do the trick.
But to be honest, I think it's a bad idea... I'm pretty sure you'll never get proper alignment between the various cells you merged together. But if you manage to do it somehow, you'll probably be a pioneer in one of the many sides of skyrim modding 
Edited by Kesta, 06 July 2015 - 11:27 AM.