Raspi and LCD
What version of Raspi is recommended for Repetier Server?
Is an LCD required. Advantages?
Good power supply
WIFI adapter (if not on processor board)
Good USB cable to printer
Least problems you have with Pi 3+. You can disable using lcd and without display even the pi zero works. So it is only that frontend reacts faster and the bigger versions have 4 cores so they are faster when it comes to rendering and leave more cpu power for print. Therefore take the fastest. Also when slicing comes they have more ram to slice bigger models
LCD is not required and only works in pro version. It is nice if it is close to printer so you can control printer from the touchscreen, start jobs and stop them. Alternatively you can also go to printer with smartphone and web frontend running.
You also will need a housing but there are many stl files on thingiverse to print them on your own.
A cheap tablet in Kiosk mode mounted beside printer(s) makes for a very nice setup