Some things I've thought up so far:county zoningcounty building permit processeasementswater table (there's no water/sewer/electric)But really, short of talking to the listing agent who I imagine is primarily motivated by sealing the deal, I'm not sure what sort of due diligence I should engage in.

Well during that time you haven't got a buyer locked in and you may want to start the clock over to give you just enough time to seal the deal.

Awesome testimony Andrew Davis The house is big and for that price, good score and I learnt something from your story that I will take into consideration when I do a deal...that there are times to offer higher than asking price to seal a deal if there is a lot of competition so thank you so much for sharing and all the best with the project as a whole!

Also, if the improvements are not permitted...you might trylooking for a "Certified Structural Engineer" to inspect the home first.If they "Wet Seal" the home as to code...The County will likely HAVE to issue you a permit for the improvements regardless of when they were done.In NC, anyway, a Certified Structural Engineer" out ranks a Building Inspector in every regard. 

@Dmitri L.Is there a single layer membrane (either sheet or rolled/painted on) underneath the shingles to seal the concrete?   

I better pick one soon, or my fate is sealed.  

Inspect regularly.Exhaust fumes go somewhere.Inspect the garage to make sure it is properly ventilated to the outside and not inside the house or to the attic.Make sure the door to the house closes correctly and seals.  

Then tile, grout and seal.

I may put boards weighted down with bricks on the leading wind edge side until they seal. 

For example do i need a business license, Corporate Seal and compliance kit, permits, tax registrations and operation agreements.