Dude, it's difficult to me, I watched videos but idk how to import a world from a MC world on Mine-Imator. BTW, I've gotten used Flat world because it help me to add many RANDOM things on a Flat World, hehe.
When you start a new project, the location to make things is on flat overworld, and then, you add things on ModelBench(Player, Mobs, Scenery, Item, etc).
Idk the flat Nether dimension will be good. The Mine-Imator gives you a flat infinity world to do animations and/or renders. And it's difficult to add new custom sceneries.