About your import problem, you should check if in the import window detects the tiles resolution, if not this means your WM sizes are not correct, just follow my guide.
Also always remove your imported tile levels from the Content Browser before you re-importing the same tiles! Otherwise you’ll have a mess.
Regarding the tiled flow map I’m afraid I don’t know the correct answer. I’m just two steps ahead of you. But this a good one.
By the way, if you export your tiles in WM in steps and you want to import it progressively into UE, at the moment I’m havving the issue that the new tiles Z is shifted with almost 2000 cm! This is a mystery!