For further background, I’m looking to purchase a spot around 750K, but want to seller finance 100-200k of the price to reduce the need for a large down payment / keep myself liquid for renovation costs. 

I've been doing a deep dive looking at cash on cash return for various down payments and expenses on properties with a mortgage.

I also wouldn't recommend trusting a seller to do any long term fixes.

The more money you save, the lower your monthly payment because the more you can put down.This is really great advice....some of the best. 

That allows the payment to be low, manageable and easy to cash flow when you transition it into a rental.When you move out you will have more money in the bank, stronger assets, and be cash fluid in case you need to make an offer on more investment properties.

I would set up a family trust, if you have a ton of equity maybe you refi the properties into an LLC but if you are locked in with lower rates then I wouldn't touch the ownership piece yet. 

Bring in a trusted contractor : to assess the current property and how much will it cost to get everything up to code (if any)... 5.

We have tenants that we have repeatedly put up 7-day curables but we do not want to lose them as a tenant.As for not paying, follow your systems for non-payment just like rent.

Other than that, I'm not sure what to recommend except maybe team up with Lynnbrook for payments outside Airbnb.

i'd advise you to network your way to something - you need people trusted by people you trust.