@Sophie Maisel all 15 amp and 20 amp circuits should be afci protected and in some cases like you’ve mentioned “close to water” or unfinished portions of the home that should be gfci or dual breakers afci/gfci but this is on “new construction” I would have thought a panel replacement would be required to follow code though but not sure.

  $12k for dual Trane units! 

I did Dual Enrollment during high school and completed a college course Speech class. 

A 50/50 split may be fair to you guys.....but I would never be the one putting in the money into a joint LLC.Anytime I'm 100% of the money, I own the LLC 100% myself and just create JVs or profit share deals with any other person I involve.You can certainly form a dual member LLC, or an LLP, but you need very clear operating agreements, corporate resolutions, etc.  

The place has dual exterior storm windows.

It would be dual house hacking, while you rent out the other two units. 

A quality Voltage meter is an absolute life saver, I have a craftsmen Volt meter I bought 10 years ago for 75 dollars.

As far as I know, low voltage lighting ran how you are doing it is a big gray area as far as the electrical industry is concerned.

Improvements:  ADDING new features or upgrading an existing feature.eg:  Old window may be a single pane casement style (crank to open) and the upgrade may be to a dual or triple pane, eGlass with Argon fill replacement.That's an improvement, a capital expenditure and amortized.

They are line voltage halogen hockey puck lights installed by the previous owner, and half of them do not work, with incorrect wiring.Trying to decide what to do with them, this is going to be a rental.Are cabinet lights a desirable feature?