How far is too far, the windows are single pane but everything else we can do for about 15K.

Only the frame holding the glass is replaced - - it's called a Z-bar frame.If you're doing replacements, by all means upgrade to dual-pane, E-glass and make your investment worth the time and effort.

To me I'm thinking this is not make ready work or get it rent ready work....replacing the panel is renovation work.  

.), it could put a very large strain on your relationship.

Showers are all cast iron tubs so I'll re-tile the shower surround, then professionally spray the cast iron tubs.The whole building has been re-roofed with a TPO roof and all windows have been upgraded to dual pane vinyl windows. 

It's in a fantastic location, perfect for the type of tenants I'd like to attract. it seems the electrical panel is a mess.

My main worries are the extra wear and maintenance on the pump, the electrical usage, the "strain" on the well itself from a large fill (if any, I don't know much about wells.

Make sure he has access to common area where electric panel is so if he has issue he can reset breaker.. or any other utility shut offs.. hitting a water pipe or blowing a breaker isn't planned but a quick reset or shut off is easy if you can get to the area. 

If the relationship with the tenants is so strained that we can't walk through that house needs to be bought at a deep discount, as those tenant issues are being passed along.

Or who knows, maybe he knows of a better source, one that doesn't strain the relationship of your "most valuable connection."