Not a right or wrong answer based on your investment horizon but a good tool to use.

First of all, I suggest you search the forums as arbitrage has been discussed ad nauseam.

Here are a few suggestions on how you can maximize the wealth of information available: Check out the blogs and podcasts, or take advantage of the search feature (magnifying glass).

BRRRRs are a useful tool for the right scenario, but it sounds like you have the opportunity to buy a house with basically no cash in, and with probably some of the cheapest financing available.

Be sure to check out the free tools BP provides to help analyze deals you may have and also market insights.

Seller financing is just one tool of many in how to finance a deal.

If there issues that need to be worked out with the 6-unit property, I would utilize that as a negotiating tool to work out a seller financing strategy with the current owner. 

I signed up for a 7 day free trial to try out the tools, but I forgot to cancel on time.

Most serious and qualified tenants are searching on the major 3rd party platforms you mentioned + realtor.com, redfin, and a few others.Apartments.com & homes.com are owned by the same company and may offer some additional marketing options.Another strategy to consider here is social media - video marketing.

And a quick search U find they have no license so you know they are fakes without going any further..