I recommend the tape measure trick, much simpler than a traditional drag chain. I drew up a bracket to attach to the roller plates: Cable Chain Holder
I don’t think there’s any point supporting the mid point of the tubes, vertical movement of the frame isn’t a problem.
I used the ‘minion’ RAMPS case, but I’m not sure I’d recommend it, the adjustable angle LCD is more annoying that useful, and some of the holes needed modification. It’s ok, but not as well designed as the V1 stuff!
The most useful thing to print might be some clamps
Vacuum duct depends on your router - what are you using?