I wonder if there's a proper way to rent out rooms or "units" without having to chop up the house and adding separate entrances and meters.

You should also check that the seller has proper chain of ownership of the mortgage.

Or do I just need to make sure that the contract is worded properly and protects my interests?

The tenancy is held until they return the premises to me and/or a properly obtained and executed writ of possession from a judge sets them out on the curb.Your state laws may vary.  

Proper slope away from a house and gutter extensions can solve about 90% of foundation issues caused by water is what I have learned from my foundation guys.

Just give proper notice and go.You have a key, right?

I would replace the exhaust fan and make sure it is properly connected. 

Sometimes your desired data is easily accessible and in a proper format but more times than not you will get the run around in search for your data and then when you finally get it, you will need further assistance getting it market ready. 

If they occupy, you treat them as an unlawful occupant without a lease and give them the proper notification under the law. 

I definitely will keep on doing my personal research as well as managing proper information.