I would ideally like to transition fully into real estate investing in the next year, possibly by supplementing with a few traditional real estate deals once I pass my real estate licensing exam and get sponsored by a broker.

Budget for all of the direct and indirect expenses.Be comfortable hiring others to supplement what you do.  

If it is cash flowing negatively already, you are already supplementing it now with your regular income.

Hi BP,I'm trying to help my parents find a income property to invest in to supplement retirement.

Meanwhile the other tenants will be helping pay your loan (ideally partially supplementing the cost on your unit).  

I am a teacher and have two fellow educators who plan to working together to flip a house this summer to supplement our income in the short term with long plans of getting out of education sooner than later.

If you just want a half a dozen free-and-clear rental properties to supplement your retirement income, then pay them off (especially if deals are hard to come by or the numbers don't make sense).There are many people on BP that haven't been in the real estate game long enough to have weathered the 2007-2008 storm with substantial real estate holdings, so be leery of taking advice from these people when it comes to risk and leverage.  

The guys who want to retire; they aren't in a hurry to sell/not desperate, but like not having to pay a Realtor, AND they are interested in seller financing to supplement their income.

There is zero logic in supplementing any tenants rent out of your own pocket.

My guess on the deal you're referencing would be that there's a 6% pref with a 2% accrued/catch up, in which case the accrued would be caught up during an equity event - refinance, supplemental loan or yes, the sale of the property - for a total of 8%.