I would keep your environment in UE. UE was literally built for rendering environments. TouchDesigner can render environments, but there’s no comparison to UE in terms of render quality. It’s like comparing a screwdriver to a power drill - nothing wrong either either tool, they have their places. TouchDesigner is an incredible screw driver when it comes to rendering, and Unreal is an epic (ha) power drill when it comes to rendering. But like any tool, it depends on the project. You wouldn’t use a power drill to open a phone, and you wouldn’t use a screw driver to build a house.
We commonly use plugins like OffWorldLive: https://offworld.live/ to pipe video textures from UE to Touch and Touch to UE.
TouchDesigner is far more straightforward than UE for:
-External device integration (Kinect, lidar, AJA, etc.)
-Projection mapping/display outputs
Really, think of TouchDesigner like blueprints on steroids. I would suggest using Unreal for the frontend (the environment) of your project and use TouchDesigner for the backend (signal processing / display routing / etc). Both have their strengths and weaknesses.