Hi, Im new here...I know this subject as been done to death.

(Subject To?)

Unrelated, they also used soap in our hot tub requiring extensive cleaning.

But, I love "arguing" with you about such things, because there is no right answer, in my opinion, and you always have good and well supported thoughts on the subject.

If there is a 1st lien in front of the Foreclosing lienholder, the sale will be subject to the 1st mortgage, and regardless of how much you or someone else bids on the inferior lien you will still be responsible for the entire payoff amount.   

It seems like it has the potential to be a decent house hack where I can live in one side and rent out the other side, but I am analyzing it as if I were renting out both units.Here's the overview:Seller accepted my offer of $90,000 (they were originally asking $95,000)Similar sized duplexes rent for around $1,500 total ($750 per unit)The total gross rent would be about 1.6% of the purchase price.I can get a conventional 30 year loan @ 4.5% interest, with a 5% down payment.Mortgage payments with PMI would be around $469 according to mortgagecalculator.org (not including taxes or insurance)Using the 50% rule of thumb to estimate expenses, I might be able to cash flow around $140 per unit.Here's what I found out when I went inside:There are 2 new forced air furnaces.Updated pex and PVC piping.Updated electrical wiring with separate panels.2 old corroded hot water tanks.

You might be able to guess it is a hot button for me.

Be it a hot market or a slow market, you can't go wrong if:1. 

... as my wife reminds me about taking another "hobby" too far...hah)Anybody know of a good post on this subject or even a book?

If this was a property you were seriously considering, I'd call a local lender or two and ask for a rough estimate.I'd estimate about 15% for Capex + Repairs.Vacancy is a pretty subjective measure and depends on the person.