Don't use two boards, isolating them would be a nightmare and far too esoteric for a school boy. Repetier supports printing and CNC. Don't use RAMPS, you'll end up pissing away that money and then buying a real board. The cost for a CNC spindle is around $100 for even a cheap POS Amazon one and that's not including the speed controller or any machining related equipment such as gauges or bits.
I'd settle for a large form printer and upgrades over time.