Desperate @ 2am I text him & the next day he went in & replaced the HW tank, electrical sub-panel etc.

probably not and trying to charge them for repairs due to their neglect is difficult to prove unless perhaps the tank is pumped upon move in with professional inspection report and then a new inspection shows negligence through behavior they were educated to not commit.

The third is a backup.City water/sewer, no septic tanks to worry about.Window AC units.Concerns:While current manager has kept occupancy high over the last five years, he admits to not collecting security deposits.

If Septic, how old is the tank and can they provide proof of last being pumped?  

I am a newb as well so I'm not sure how to advise on finding that out but try to ask local investors is the first solution that comes to mind.I also think I know a big issue with the 203 loan is making absolutely sure you asked for enough money for repairs because I don't think you can get additional money for repairs but even if you can the government probably takes forever to get you that cash meanwhile you may have empty units because their arent livable meanwhile you are paying off a mortgage, taxes, etc.When you find what you perceive to be a deal make sure you post it on bigger pockets(not the address) so the sharks can tear it apart haha!

I'm a circling shark.

He replaced the old water heater with a big insulated tank fed from the main boiler.

I am pretty confident that the market in Denver won'd tank, it's going up 10% per year for the last 5-6, and shows no signs of not continuing that trend. 

^ In addition to Zillow there are CyberHomes and Property Shark (both free the last time I checked).

Many of them then lost everything they had, including their primary residence when the market tanked and that house was worth 150k again.