With that said, I may be looking too far ahead but I like to plan as much as possible so that I can avoid slowing down or preventing a process in the future.

Of course life happens and not everyone that "passes" the screening turns out to be a perfect tenant, but as the landlord the risk prevention starts at square one.

Is there anything I can do legally to prevent them from doing so?

A lot of commercial/bank loans come with prepayment penalties to prevent this from happening, but you shouldn't have that with your hard money loan. 

The buyer does their due diligence by ordering the title work, which is done by the title company, who in turn insures that the home’s title is free of clouds or defects such as judgments, liens, bankruptcies, condemnation etc. that would prevent the seller from transferring clear or marketable title to the buyer.

This can only be lifted in matters where it would be necessary for you to sell or refinance i.e. job moving, death if family, divorce, etc. so while appealing from a low interest rate stand point, the program is designed specifically to prevent investor usage.

They also work well when properly installed to prevent moisture intrusions.

The LLC question though is a small detail when it comes to your overall investing, insurance and generally being a good land lord taking care of the building SHOULD prevent most of those problems.

You typically want a cover on the outside to keep out rain and snow, then something inside or outside to cover it with insulation and prevent the cold from leaking into the living space.Second, I would measure how cold it actually gets.

I would also recommend a second opinion from another plumber, but it sounds like your time limitations may prevent that.