@Matthew Cook I would NOT pay for the renovations unless I was on title or had a very formal contract written about the split of profits.

*As a side note, I think maybe it would be fun also to try and identify where new technology or machine-learning driven approaches could increase efficiency in the spaceAs for my financial situation, personally, I have around 50k saved but 20k of it is tied up in assets I don't want to pay capital gains tax on.

The perceived value may be more, because you know an STR was run there and making money, but a lender wont value it more.While I agree a lender probably won’t value it more, an investor interested in running it as a STR will pay more.  

@Sunny Wu of course the tenants don't want to pay!

I think the LLC also makes it easier to open a local bank account, which is convenient to pay utilities or other local bills or your property manager, etc.  

It may sound nice to pay a 6% management fee but the extra fees can add up to be more than the other company that charges 10% with no additional fees.

Quote from @Sami Gren: I start by making the original tenant fill out a form requesting to add a new renter, and they pay me a $50 processing fee (I charge a $50 fee any time I make changes to an existing lease). 

This is what blows my mind about the cults of seller finance - they teach you to pay anything for a home because you can put little money into it.

If I pay down $50K, how can I calculate the new monthly payment?

You would need to let them know you are 2nd lender and want to pay the loan off.