Yes, I have answers to all of this but they are for too lengthy for a forum post.

We are told that a big one is overdue in state of WA so I carry them...but it's a high cost.

I won't be even the slightest bit perturbed if you decide not to read my post.The first thing to address is that (at least in Texas) the estoppel certificates are going to be written into the purchase by the title company, so that the overdue rent is not your problem and is quite frankly irrelevant to you from the perspective of completing your purchase. 

Everyone's jumping on the "raise his rent that's reasonable" train....But we're also ignoring that he said this property is 40 years overdue on updates and such???? 

Tenant proof your house (smoke alarms, fire extinguisher, locks, door stops, fix overdue maintenance).3. 

My mother recently passed and I can tell you that the many, many letters I received from investors have all been extremely irritating.But, in your case, as it's been a few years, at least it won't be like the others who wrote letters supposedly of sympathy before she was even cold in her grave, then wanting me to sell her property to them for far less than it's value.Knowing what these people have dealt with regarding the above and possibly a lengthy probate, etc., should be helpful. 

I also agree with your lengthy discourse.

Don’t overdue the rehab.  

In those situations, the original owner could have a lengthy right of redemption that extends far beyond the sale.

Likely after accepting your general terms like price, financing, closing date, emd, etc, the bank will provide a lengthy addendum.