This painter previously corrected a poor drywall installation of 2 walls and painted with Sherwin Williams small drywall, which looked  good to my untrained eye.  

Lastly, when i try and call them to speak to my property manager 99% of the time I wind up having to submit a note in their portal and wait for a call back.As to to the new garage door that will be installed by the tenant, I wish they would be more involved, giving the tenant some options of companies to call, and to walk them through the repair process.Am i wrong in any of these thoughts or concerns about my current PM---or---do i need to let the property manager do their thing and learn to take a step back?

He will know if the heater is even installed correctly, safely, and to code.

If it cost you $5000 to install, use that as your starting point.

If you had a default interest clause in your promissory note and didn't enforce that and they still made monthly installment payments, for which you accepted each time, then you are in a sticky situation to require additional extension costs. 

Installing a GFI at the top of each circuit is ridiculously easy, as you say.

What about a well and solar system?

Cutting tiles can be a challenge if you have angle and corner pieces but a basic install isn't too hard.

Insulate, add electrical, mini-split ac, and possibly plumbing, as desired, drywall, tape and paint, put built-in cab's on one side if you want, hang the tv, speakers, etc, install bi-fold/multi-fold doors on the side leading to a patio, and replace the garage door with an insulated one keeping the track and removing the motor, or install a carriage type garage door into the existing garage opening.

Here is the specific language from Assembly Bill No. 68:a local agency, special district, or water corporation shall not require the applicant to install a new or separate utility connection directly between the accessory dwelling unit and the utility or impose a related connection fee or capacity charge, unless the accessory dwelling unit was constructed with a new single-family home.If the Planning Department is telling you that you need separate utilities and you're adding an ADU to a lot with an existing SFR, refer them to the above language from AB 68.