New furnace good for 15 years.Contractor recommends 80% (for a rental) because of maintenance issues with extra venting and water condensation that needs to be removed.

If they are saying it is lower, I would definitely do extra verification with the employer.  

They also offered in-home plumbing support for an extra fee...but I cheaped out because I have a 3-unit building and would have to pay per unit. 

Some are fantastic and pay extra special attention :) 

Rent out your extra rooms and live rent free.

What have you learned in placing tenants, and what sort of extra lease features/common sense did you do to keep the peace?

I got 2nd position line of credit on it for 55k and advanced on it to get my cash out (20% down or $40k) and then some (an extra $15k).

I wish life worked that way....Costs you need to understand from your servicer are boarding fees, servicing costs. if there are extra costs for tax and insurance escrows, if their costs change if the loan becomes non performing, how much $$$ to send a notice of default for non performing notes, and how late fees are handled (I have seen some keep all late fees, some split them 50/50).To calculate yields I use the 10bii app.  

I'm cringing at the extra interest $ paid over time.

It doesn't cost you anything extra to navigate the sale through the agent.