I wouldn’t paint the inside at this point. Wiring eb modules would depend on which driver is attached, but not difficult. Once we know exactly what you’re working with i can cover this with you.
The eb gen2 is available in 280mm, 560mm, and 1120mm lengths. If you want to mount to sides the 560mm good choice. But if you want to top mount they would be too large, 280mm would probably make more sense.
Here is a link to a small build with eb strips. Should give you rough idea