I like the idea of a lender looking at the deal and not pulling my credit (again), but I'm wondering how paying such a lender back would work, considering a (likely) higher interest rate and short amortization period.

@Ruth S.Most private lenders only do short term and do not like being in second position especially at 100% ltv.

My goal is to build up a strong portfolio of long term rental properties that will generate cash flow which I intend to use for reinvestment in the short to medium term, and to enhance my retirement cash flow in the long term.

I am not a seasoned investor, but I have learned a lot in my short time. 

Eg if doing a short term rental, don't assume it will be rented all of the time.What do the numbers look like if you took that money and bought a home as a rental?

I am a newer investor (currently 1 short-term rental in addition to my primary residence) looking to purchase a property that I will make into a short-term rental. 

Don't be swayed by short-term trends or succumb to pressure to make rash decisions!

Dodd Frank will apply...see below.Not More Than 3 Properties Exemption Any person or entity cannot provide seller financing to an owner occupant more than 3 times in a 12 month period without using a MLO (mortgage loan originator).

There’s a short but informative book written by @Dave Foster as well as some YouTube videos.

It's a short term product with interest only payments and no pre-pay penalties.