This is a issue that for me is a deal breaker when investing in multi units.

Non traditional income is not a deal breaker.

For example, are there any deal breakers you'd be on the lookout for; any damage/mold/etc. that would be a dealbreaker?

I think that modern electrical code wants the dishwasher to be on its own circuit... you're not supposed to tap the circuit that serves the countertop outlet to the left of the stove, because that should be one of the two 20 A kitchen circuits.  

This is a total shock, the last email I got from him he asked if I wanted to terminate early as he wants to 'do some major repairs and upgrades' and I'm just short circuiting here.I strive to be a good tenant.

After a big decision in the 9th Circuit in 2012, I believe most legal experts are comfortable saying that a roommate may discriminate based on gender.

Because of the furnace, breakers, etc., you probably can't really lock everyone out of the basement.

These wires, still on an energized circuit, were only discovered during the inspection, nearly a year after they were cut.

I would bring all knob circuits into a new 100/200 panel and add new circuits to kitchen (min 2/20amp) and baths (min1/20amp)  Also 20 amp cicuits to garage basement or outdoor areas (all grounded). 

If someone isn't paying for months, and is basically saying "F you, you can't get rid of me", we're turning off their water, pulling their meters/breakers, shutting off gas, etc.