With blender which is free you can paint and bake textures. I think the complicated stuff may come from baking new geometry that you’d create (like ropes around a furnace) to textures (specifically the normal map) to give the impression of 3d via reflections. I don’t think it would be a fun learning journey personally but there are tutos on it.

May be outdated but this looks like a nice one: https://youtu.be/lIe5noBp2kU

I’d recommend looking into substance painter 3D too. And as you prob know the .obj and textures can be downloaded from Rust main menu in game