Does TileED work well with Mesh Combine Studio?
I have no idea. I have never used Mesh Combine Studio. It should not be a problem though. I assume that tool will take all placed tile objects and combine them and remove the originals from the scene. That is not a problem since that is what TileEd do itself in its own mesh combine. While you want to edit however there should be tiles. You can easily restore the tiles, and remove the combined mesh, if the tool does not mess with the parent Map object which provides the whole inspector. Check out some videos on TileEd; there should be something about how I do mesh combine.
Is there any Art Guidelines to making custom tiles for TileED
Ye, check the docs and videos.
What is the minimum version of Unity that is supported by TileED