I know handymen that can do the work probably cheaper, even on advanced stuff like electrical panel changes.And who should I use for insurance?

If the main panel is split into two primary circuits and each of the two circuits serves a sub-panel in each apartment, then you could have an electrician install a eamon demon sub-meter on each line that is serving the sub-panels. 

Oven not working is usually one of three things... defective element, do it yourself cheep fix, fuse, do it yourself cheep fix, computer control panel, replace with used appliance...$200..  

You can also look inside the panel (or have someone qualified do that) and see if there are any Al wires.You can look at the other end (fixtures, switches, outlets) but this may not tell you as it was/is common practice to pig-tail copper onto Al to allow Cu fixtures and switches to be used (they are far cheaper).  

Electrical Panel - Sometimes these are located outside you can you take the panel off to see if the breakers and wire are up to code.4.

All new paint, flooring, plumbing, countertops, electric panels and some appliances (approx $3k/unit). 

As a bonus, I found a secret safe on the second floor behind a sliding panel!  

But for bigger work, such as changing out the electric panel, HVAC, sewage pipe etc,  I suggest you hire the licensed, bonded and insured.

Watch out for Federal Pacific panel boxes.

I will be there and will be on an investor panel that will be answering questions from everyone.