Don’t go into to much detail of your personal assets and worth, etc on any public forum as you have no attorney client privilege protection and can deem to have waived it. 

Pressure the city to sue for maintaining a public nuisance.

The only place you should note assumable mortgages is in the description or the agent notes on the MLS, not separately on a public portal.

Owning multiple types of multi-family rentals (Class C and B for now), I have a good grasp of the value, in addition to just public rental data, so not really a problem for me.

Active foreclosures are a matter of public record. you can search county records, public notices in the paper and so on. you won't find any list of delinquent borrowers that do not have a filed action, anywhere as that is not public record.

There were over 60 units vacant for some time and were only able to unload half at a public auction, leaving another 30 units vacant.I bought one unit for my sister as an owner occupied unit with her bidding at the auction.

Choosing Between 506b or 506c: Both have their pros and cons. 506(b) allows you to raise money from accredited and up to 35 non-accredited investors, but you can't publicly advertise. 506(c) allows for public advertising but only accredited investors can participate.

It is all public information, so technically it is free to get, but the Ttitle companies put it in a useful format.  

The lawsuit includes claims for breach of contract, specific performance, and trespass to try title, and the case is registered in public records.Additionally, the lender has initiated foreclosure proceedings on the property due to Seller Z's default on payments.Is there any action I should take as Buyer A?

Better than an amateur evaluating a place and guessing what's wrong, not likely to miss something big after training, but really not qualified to tell you if X property is likely to make steady money as a rental after you fix what's obviously wrong or Y property is just going to be a total money pit.It's not like you and the roofing inspector/public adjustor space, where you go toe-to-toe against the insurance companies for real money.