YOu can search around and get an idea of the head for the sum of all of the zones on a pump...then, you'd select the pump required to overcome that head. When balancing loops, you generally run the longest one full open, and then start to throttle the shorter ones, more as they get shorter.
It can be hard to know for sure when you've gotten all of the air out of a loop when there are elevation changes...you need enough pressure to force water through. If the pump doesn't have enough head to move the water with the air trapped, you need to add pressure from the water supply to raise it. Note, though, every time you add potable water into the system, you're also adding minerals and some trapped air. That trapped air is what can cause corrosion inside of the system. If it is truly purged of all air, any dissolved air will end up rusting things, but once used up, that stops and does not progress any further. Once you have all of the air outside of the system, it doesn't take anywhere near as much work from the pump since when some water is going up, the same amount is falling down to help carry it around the loop(s). Prior to that, it has to have enough head to push it up over that high point - that's where you may need help from the supply system's pressure and volume. I've found that running the discharge from trying to purge a loop into a partially filled bucket of water via a hose lets me both see and hear when it is running clear with no air bubbles. Essentially, you continue until it runs clear, however much time it takes.
