A big issue you might run into is that most lenders will require you to qualify carrying two mortgages in your debt-to-income ratio.

I have a project where the seller is carrying the note on the home with a 20% down payment.

Long term it would pretty hard to make a descent profit on a rental that was carrying a 9% loan.  

App folio has a dashboard home page that shows cash in/cash out but it does not show the balance you may have carried over from the prior month. 

(Long Days on market) and then using secondary financing for closing and carrying costs.

Although NARPM may not be widely known, it still carries significant weight.

You could also do a subject to with a carry back for the difference.

There are  additional fees incurred investing this way: membership fees, fees to maintain the entity that carries every deal you get involved with and possibly other non-disclosed fees. 

One brand new SFR with brand new Carrie and air handler's noise level reached 90db.Brand new Lennox with one SFR replaced leaking coil twice in 3ed and 4th year.Few Goodman, already there or new.

The rest was carrying costs: utilities, insurance, purchase and sale closing costs, and interest payments on the loan.