It's a huge unknown to be putting in so much work/money. 

Lot of unknowns here.

Obviously, the unknown occupant can lead to trouble in some cases, but again, you have way less actual control over this versus when you are screening the tenant. 

But a certain amount of fear of the unknown might cause them to feel they HAVE to pay for something worthwhile.

How much should I budget for unknown repairs and other unanticipated/unexpected costs?

I expect they will, the other unknown is will people feel more comfortable staying with a corporate entity or an AIRBNB?  

As Ellis San Jose mentioned, anyone who thinks the worst case scenario is that they'll receive 2/3 or liquidated proceeds is incorrect.In dealing with a pre-probate scenario, the decision must be made if you intend to buy the asset, buy heirs' or beneficiaries' interest, or merely focus on plays that make a profit.If you buy the interest(s) and probate the estate yourself, you become the PR and have the exposure to all known (and unknown) heirs and creditors as the fiduciary.

Again by asking around, you can find out how much.Asking about the marketability of land at an unknown address with vague parameters is a bit like asking how much a car is worth. 

Is there enough cushion with your purchase price and estimated repairs to allow for unknown issues and still get in under that price point.

I feel like I am at the point where I am ready to step off the cliff and into the unknown with my first property.