Hey there, here is the full honest answer:
I was totally motivated about 1 year ago, I recreated half of Myst Island, with some crude day-night shift and what-not. But the terrain really caused me some trouble. It was just too complex to re-create the whole myst island with tessellated boxes. To get rid off polygon errors and smooth build.
Later I tried to recreate channelwood, I laid out the whole basic level and built the stone island. But then the darn Unreal-Editor did it's job again and crashed and messed up my file.
After that I was pissed off and didn't care at all anymore.
Just like old times

But recently I started becoming more interested again.
The biggest trouble at the moment is the terrain is messing up polygons using heightmap-mesh and needs complete recreation using tessellated boxes. The terrain cause me too much work, but most of the buildings and objects are done.
Also the big tree-elevator which is working, you keep falling trough the tree, unless you're inside elevator.
There is some collision failure in the tree-evelator mesh I can't get rid off.
Thank you, I can upload map files if anyone likes to work with them.
I also got a real 1:1 Myst Island heightmap to work with.