There aren’t any needed mods. I would suggest building it stock first, and then you’ll know where to put your energy. You will rapidly become an expert on your machine. Most mods are trivial to add after the fact.
The one hint I will give you is to build you table bigger than your machine borders if you plan on messing with cable chains, because they extend out a few inches.
I’m doing the cheap cable management with tape measures as guides and cable sleeves around to make a neat package.
A holder for shop-vac is handy unless you want to either have your room full of dust or want to sit there manually tracing along with the hose…I’m currently using a household paper roll zip-tied to a wooden stick (not nice but works)
Some sort of enclosure for your electronics keeps it nice and tidy and hopefully dust free. (I use an IKEA plastic box)
LCD holder would be neat but I have not yet seen any that fulfill my needs.
I want to spend my free time now to print what I can also, I want stuff which will make my life easier in the short term, such as the vacuum adapter and the wire management stuff.
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?
That link should open OnShape in your browser, from where you should be able to export an STL (or copy the design and make changes). Here’s the STL (zipped to keep the forum software happy).