Right now the plan has  PAC-CLAD ACM PANEL all over, which I think is overkill, the facade definitely, its beautiful, but I think the architect used way to much.

OSB vs Other type of SIP panels (fiber/steel), pros and cos?

Planning desk will tell you what is needed, get a contractor to cost it out because it is not just getting another panel, you might need to bring wiring up to code, and plumbing??? 

Depends on: what city or county planning desk thinks; was the construction done to code; does the addition appear visibly to code; electric panel up to date; unit has heat...Garage conversion is not an ADU per se.How old is the subject?

If you're upgrading to 200amp panel the odds are against you.

I thought @Tina Sandoval did a great job on the panel.

=======Locate the septic feild(s)(s)(s).Have a scientific drinkability test on the tap water for any contaminates.Beware of big (and small) spiders in the basement.9 x 9 tiles are probably asbestos, same for the glue used to hold them down.Wiring and electrical panels may be at end of service life.Florescent lighting may be circa 1960 (I dream of Jeannie) lacking modern non-buzzing startups and be way to many for modern use (electrical hogs).Don't drink any of the water (or even get it splashed on you) without having it tested first.The building may have city water and well combination.Find all abandoned septic fields.Find out if the fire suppression equipment is up to spec with the local fire dept--inspections, types.Without a roof and with many broken out windows insurance may be hard to find.Paint--expect lead (the pealing type) of paint.Assume anything with capacitors-(HVAC, Florescent troffers, Kitchen electric motors, food service garbage disposals, etc.. )-the capacitors are bad--do not turn on until checked by a competent technician.Look for a basement.Look for fallout shelter(s)(s)(s) underground separate from the building (Duck and Cover Turtle era).Look for steam heat system and have it inspected for possible use or demolition.Look for abandoned wells, that may have dried up or were too contaminated to continue use.A phase 1 enviro would have been a good CYA move--you can bet any buyer from you will get one...Pay to have a written professional inspection done of the building to get a consolidated look at the things you will be facing.

Other things like the solar panel, you may not have known enough about to know it produced more than you needed (which is actually a good thing as then you get money back from the electrical company even if that goes to paying other utilities).

Had to replace outside electrical panel as well.Literally had a $30 an hour handyman work nearly full-time at the house just trying to stay ahead of the corrosion and humidity issues.

With some of our solar panel lenders for example, you can go as low as ~3.99% (with a high upfront fee) up to ~9.5-10% with no or very low fee. hope this helps