TL;DR of the post, generated automatically.

OP has been learning Unreal Engine and tested how pre-rendered retro-style backgrounds would work in it. They say the basic idea seems to be working.

• Method: The environments were modeled in Blender from the camera view, with camera height, position and focal length eyeballed. UVs were projected from that view, and parts were made transparent in GIMP where needed.
• Setup in UE: Lights and the camera were placed at roughly the same positions as in Blender, and each camera view was grouped to keep the setup tidy. The image texture is used for both surface color and emission, so the backgrounds look bright but still catch shadows.
• Known gaps: The game mechanics are still very primitive, the camera switching blueprint is not reliable, and only the default mannequin and animations were tested.