If a seller refinanced a house at around 220k and has about 120k left in mortgage, but the house also appreciated to 450k, how do I structure a subto/seller finance deal?

I own a house in North Port, Florida (right on the border of Port Charlotte).

I'm considering partnering with a non-profit that would manage the sober-living program; with me just providing the house passively for rent on a per bed basis. 

The unit shares the same heating and cooling as my own house.

Is he just looking to have no house payment?  

If I was to trade a $300k house for a $310k house that will cost me $10k and $347/month what amount should I ask for to make up for these losses?

I fear the lawyers will become wealthy over this litigation...Overall, it's an interesting "solution" to the problem of foreign investment in real estate and the lack of adequate housing for the population. 

A great way to get started if you currently have a W2 job is to buy a house hack like a duplex or a fourplex where you can move into one of the units and continue to rent/manage the other units.

It's in great school districts, so I just listed those in the ad in a neutral, factual manner, which I believe won't violate fair housing laws as long as I avoid implying a preference. 

Your plan to house hack a multifamily property in Indianapolis is a great strategy to start building equity and learning the ropes with manageable risk.