Edit 10/17: See comments for update.
I've looked high and low for a external mounting panel for the Ender 3 board, with no luck.
My goal was to have all the extra crap that I've added onto my printer, moved off the printer. They don't make AIO extension kits for the Ender 3 so you'll have to make your own cables.
https://www.amazon.com/gp/product/B01IS1N5KY/ - LCD Screen
https://www.amazon.com/gp/product/B01BQUSQNU/ - Raspberry Pi Camera
Please let me know what else you would like to see.
The only supports required are for the mortise joints (well, it was a mortise, now it's more like a lap joint).
Any board with tenon (the male portion of the joint) can be printed with supports off, but it will not influence your print either way.
Mount all boards with M3x4's (except RPi, which is M2.5x4), assemble printed parts with M3x8's. These screw into brass inserts that you "melt" into the board using a soldering iron to heat the insert enough to embed it in the plastic.
You can find the inserts here:
Set of knurled inserts: http://a.co/d/7CDOWAh