That will ensure you are making very large mistakes that will cost something like a $100 of whatever just cause you didn't think to add it as a negative. 

FHA, since it's such a low down payment, is going to bring PMI into the equation and that plus a high mortgage payment are going to put a real cramp in your cash flow (you should assume it will be negative in the IE)

There are a couple of different ways we can approach this type of inspection so I would love to speak to you over the phone if possible to discuss. 

I am an architect by background so I understand the importance of it, But from a 2-4 unit rehab, I can't really speak.

Most times when you buy turnkey you are buying with negative equity because you're buying in areas where investors are taking over predominantly owner occupied areas for the 1% rule.

Jason Buzi has done a lot of wholesale deals in the area and is speaking at this event this week: https://www.meetup.com/realestate-1641/events/mbcdjpyxhbwb/

Unless your mortgage rates are obscene I would just do the same thing you're doing now, with the exception of (financially speaking) downsizing out of your current home since it costs a bunch of money and makes you none. 

Seller's MLS listing agent claims not to know about the federal lien, speaks with Seller's attorney and attorney tells agent that they will be able to deliver clear title (attorney did not state how);5.

My question is; should I pay off the mortgage ASAP or find other investment properties to cover the negative cash flow? 

So not negative at least!