I would classify each of the below items as either a betterment, adaptation, or restoration, so it would fall under the 'improvements' side of the 'repairs vs improvements' argument. 

Item M in Part 1 is probably the one that pertains to your situation. 

You might want to take a look at this website to give you an idea how long items last.https://www.nachi.org/life-expectancy.htm

I invite three contractors to look at the job at a set time.I walk them through the project, give them the schedule we will adhere to and during this process I give them a list of the items I will be supplying, toilets, lights ext.

Also:- The unit failed state inspection just before we moved out, so they cannot rent to the next tenant until pending issues are resolved (they won't give me a copy of the official notice itemizing the issues), and God knows what toxins we were consuming in the 4.5 yrs we lived there.- There was no mention of security deposit being deposited into an interest accruing account, and I wasn't aware of this requirement until I started doing some research in lieu of the incident above (so I never requested this information from my end either).

My top two items that require some demo are replacing the polybutylene pipes in the unit and replacing the past-useful-life water heater on the second floor.

As a start, free online services such as Homewyze can help you understands costs for many rehab items.

What you should be looking for in your own private residence might be out of the scope for this discussion but I can comment on the other items. 

What other items should I be thinking about which would determine if it's a good deal?

Podio is very customizable so it serves as the "central hub" or "interface" and creates the relationships between items.