In a small-team scenario, I think you can expect something like Astroneer or Cube World in terms of scope. The biggest hurdle is dedicating a couple hours every day to work on it. There’s a lot of ground to cover in the engine, and 3rd-party 3D development applications. You’ll want to take notes and/or screen shots during your development time so you have quick references to look at. Took me about a year to be even remotely comfortable with modeling, and another year for texturing. But once you learn one program, you can basically jump into any other competing program with little effort. (ex. I learned to model in 3ds Max but I can use Maya and Blender fairly well).
I’d suggest starting by exporting simple objects or skeletal rigs out of your modeling software and importing to ue4. Then while you continue modeling, export and import every now and again just to make sure you haven’t yet broken anything. There are certain modeling tools/behaviors that either won’t make it into ue4 or will fail the import. It’s better to know what you can and can’t do early on than burning a month on a complicated asset only to realize you can’t use it without some serious redesign.