I have two self-installed ground source heatpump units (6 tons total) in operation since summer of 2016 with no maintenance except for the loop pump. I was using two very old second-hand pumps until last summer (one for each unit), when one impeller completely disintegrated. I took the opportunity to reconfigure the plumbing and wiring a little bit to use only one pump (more modern, theoretically better fit for my system), and it has been smooth sailing since then. We'll see how long the new pump lasts I guess.

As for loop installation, I have a few acres and dug a ditch with my dad's backhoe. Most homes around here don't even have room for a septic system, much less a horizontal ground loop. I can't speak to the cost of a vertical system, but I think it would also affect the specs of the loop pump, and not in a good way. Check for tax-incentives as well: I got a 40% tax credit on the units themselves when I bought them.

I have to edit to address the underground refrigerant leak: I haven't had to deal with this. I can only say that it would not be a fun time. I think in a properly installed and tested system, it shouldn't really happen outside of freak seismic events though, at least within a human lifetime.