Hello Eric!
5. I have been reconsidering Lyle's comment about making the endcover, the buss circuit board. We would have to come up with some suitable coverplate, over that, however, the design would be simplified considerably, albeit a little more expensive due to board area. Comments?
Given that you are going to put a shielding cover over the motherboard anyway, I'd go with your idea of putting the motherboard on standoffs which attach to a rear cover plate.
73, Lyle KK7P