I started on a board similar to this for cad.
My advice... Test whatever encoder you plan on using externally first.
I started testing parts and no sooner did I try using it I realized that I didn't like the encoder (in this case an encoder and then a trackball), it wasn't as useful or nice as I thought it would be and it would be even less useful being hard mounted to the keyboard. Later I built a board with an lcd, what I learned from it was integrating stuff into a keyboard is meh.
You're going to make a lot of compromises to make this work and then you're stuck with it, it's a lot of time/money/effort on this keyboard, what happens if your needs change or you dislike it or you simply get board (it happens a lot in this hobby)? Need special caps, have fun changing them later. Want a different switch, unless you built a pcb with hot swaps, have fun. If you hand wired, you will pretty much have to rewire the entire board if you swap switches, while easier than desoldering a pcb, putting it back together is like rebuilding the keyboard all over again. So unless this is you "end-game god tier board", which doesn't exist, something new could come out tomorrow and make you want to change it, you could get all this done only to find you hate it. Your keyboard has one job, don't go adding "stuff" in hopes of making it better.
Build a secondary housing or dock, put your dial in that, maybe add a spare usb port, sd reader, whatever, just don't trying making a keyboard do everything. It's too specialized. Anything your hands touch should be no compromise this is for repetition, repairability, replaceability.