I am still working on my own, so I don’t have a lot of details (I am planning to do a build video to help others, so that is why I haven’t started the build yet). For mine, I am going with steppers since they are a little easier to work with. The DC motors require you to add the Encoder (which is another custom PCB and components), although I am thinking of adding it anyways with the stepper for another point of information. I also think the steppers will be a little more accurate and have better torque then the DC motors.
As for the communications I haven’t played with RS485, but I am interested in testing it. So I am going to go with RS485 (I am looking at a Raspberry Pi hat that is for RS485 and sends 24 volts to the board, which I am told will work with the components in the BOM). From what it sounds like the RS485 might be more stable for longer runs then UART. I am 100% sure if that is true, but I still would like to give it a try.
These are my thoughts at least. Hope it helps.