I know there's the inspection period and buyer must perform due diligence BUT it never is normal to research permits for every single plumbing fixture, electrical box, all liveable areas, etc.

No claims, updated roofs,plumbing,electric.

So now that it is empty, I have been doing as much work as I can myself, such as painting all the walls, replacing damaged bricks, drywall repairs, AC duct repairs, plumbing repairs, and simple electrical stuff to save money, but do not feel like I have the woodworking skills needed to install cabinets or siding and have it come out looking professional and clean.

If the sponsor is buying 1980 or older make sure they have a lot of money set aside for plumbing, electrical and HVAC.

The units have had all electrical panels and water lines upgraded with permits and new kitchen cabinets installed in all units.All of these deals were on Redfin.I would argue that there is money to be made in every market.

Had a refrigerator go out.  

It has a brand new HVAC system, updated 200amp electrical panel and all new wiring throughout.

You may need permits for plumbing, electrical, and structural changes.A HELOC can be a flexible and cost-effective way to access funds for a down payment on another property. 

In my area garbage and sewer are the most common examples, but I have seen places where water and electric are municipal utilities as well.

For a flex space have you considered an electric Murphy bed?