the reservoir can be added to the Krappen AiO. but that's not an easy task. for someone inexperienced, it might result in completely broken AIO.
the pump (that is inside the CPU block) can work regardless of the liquid volume in a loop. as long as you don't add other components with hard 90 turns, the pump will be fine.
anyway, you are going to spend to spend close to 200$ which can get you a real custom loop and not some wannabe crap.