I guess it all depends on the circumstances.

I have  interested parties who could pay cash as we would not subordinate the land due to the unforeseen future.  

That would be a scenario where you have some hiccups due to permit problems or unforeseen problems...

I came up with about $10k in work so I just doubled what I'm assuming it will need to cover labor and unforeseen issues.

But having the lower payment the 30 affords you gives you much more flexibility for when life's circumstances change like if you get laid off, have vacancies, get hit by a car and can't work etc.

Best to get an operating agreement as well which clarifies who is responsible for what, what are the terms of dissolution, and other necessary items in case something unforeseen comes up.2) Yes and No.

Any missteps (forms not properly filed, etc.) then the PR under certain circumstances may be surcharged. 

Under no circumstances do we provide a signed & notarized Reconveyance until we have been completely paid off.

Does my state require a licensed plumber in this circumstance?

People's circumstances change, other offers are made, seller's remorse sets in, doubt causes seller's to be lees cooperative.