They use Debt coverage formula and not DTI.

I own 6 units (SFR + Duplexes in 30032) NO DEBT!!!. 

That's great, but you've just done THREE things that work against you: you've eliminated yourself from the radar of many buyers, you've limited the marketing on your property, and you've positioned yourself as a TARGET -- because you know who loves FSBO listings?

As part of this, can someone share their thoughts on whether debt service (principal and interest payment) is considered a fixed expense?

**** SUPER IMPORTANT- how much cash do you need to keep retained as a buffer / failsafe to service your debt (if you are getting loans) in a worst case scenario

With a good lease and solid understanding of proper and thorough screening, you can eliminate 99% of the problems most landlords have proactively.

I am saddled with student loan debt but want to build wealth and gain financial freedom.

All you do is collect a check whether it's to pay off your debt and keep in your bank account..Some office buildings if it is occupied by one big tenant may have Absolute NNN where the tenant is responsible for tax insurance and maintenance as well as structure and roof membrane of building..I am not too familiar of Office Buildings in terms of force appreciation but Multi family apartments offer that strategy..Hope this helps Good luck

Hands down. 1) less fees 2)you don’t want to start the amortization clock over again with your property in which most of your payments are all going into interests when refinancing.3)once you pay down your debt with HELOC, your credit line is available again for more draws. 

Basically how do you help a motivated seller out of a bad situation where they free of the debt?