You'll find this article to be very informative and crucial to reaching your goals: The Core 4 Members Vital to a Profitable Long-Distance Real Estate Investing Team. 

And what 'is" is a tangled jumble of things. ai will just kick back an answer loaded with "and, if, but, when" because that is how the various statutes are, loaded with layers of variables that far too often make almost any action/answer right, wrong or unknown, sometimes simultaneously multiple or all of the above. 

Have you looked into getting umbrella insurance as a first layer of defense to rentals?

My take is that it's vitally important to know who you are working with, and have the history of the players involved.

Allows more privacy and another layer of liability protection.

Your best bet is to either add another layer of subfloor (the thicker you can go the better but obviously this can cause problems for transition areas that you may not be adding subfloor to), or use either floor leveler or floor mud to help even out the floor.

Apparently this type of floor has a 6mil wear layer which is what the lifeproof from home depot (interlocking system) has.

The guy does double layer drywall and other things I would never even consider.

You basically need a 5/8” layer of type X gypsum board.

For $350 I think you might as well have that extra layer of protection.