You probably wouldn't need a "general" contractor, who (like me), would subcontract plumbing/electrical/HVAC work, though some towns permit HVAC work to be put on a general "building" permit.I'm not entirely sure what plumbing and HVAC work the previous contractor did but you may (sometimes) have issues with plumbers and HVAC guys taking over or signing off on work done by previous contractors that they can't or don't want to put their name behind (or they may charge you more simply for doing this)... depends on the company/person, and on the nature of the work done.

Accidents, electrical fires, and all kinds of mishaps are significantly more likely during rehab than during normal occupancy.

Plus our contractor told us having some of the home infrastructure there would save a little money (septic, driveway, electric).

First problem that I am working through is the knob and tube electrical in the attic(on top of insulation).

Federal fair housing law is some of the most powerful legislation on the books.

Thanks to everyone for the comments and for bringing up some items I had not considered like @Scott Mac with the amp draw for the new larger fridge.A few items to clarify:This is a SFR rental that was gutted and rehabbed soup to nuts so power for a larger fridge is fine.This is in TX and renter supplied washer dryers is common but not much else in the way of appliances.The supplied fridge is only +2 years old.I don't really have a place to put my fridge if the new fridge is moved in being an out of state REI.Tenant is unwilling to leave their fridge even if I give them mine in exchange.Tenant already has blown their deposit on repairs so there is no bargaining there.One idea I had was they could move their fridge in from their storage unit and move my fridge back to their storage unit on their own dime.When they move they either have to move mine back in or leave their bigger fridge.

The C wire provides power to the unit.

Not seeing a lot of deals these days but certainly interested in leveraging the power of many.

Oh, and we just got an email last night with them asking about replacing plugs in the bathrooms and kitchen with GFCI plugs, again, not opposed, but do we want a tenant messing with the electrical? 

It's a powerful explanation on why real estate is a superior investment in terms of both risk and return.