It's also good for insurance and legal reasons, because you will need to indicate every adult and all persons, as well as details (like children, pets, etc.), on the lease.  

The question I have, is there a legal way to assume the mortgage since he has such a great rate?

If you need financial help, ask under the "Finance, Tax, and Legal" forum.

If you evict, how much money will it cost in legal fees, court costs, lost rent (because the tenant will probably stop paying), and vacancy while you prep and fill the vacancy?

Just get a security deposit that you hold in escrow from the seller’s net proceeds (as high as you can negotiate or is legally allowable in your area, in my area the most you can do is 1 months rent) and have the sellers sign a lease/ post closing occupancy agreement like a normal tenant.

Running a business comes with paying taxes and I will work with my CPA to write-off/depreciate whatever I legally can as a business owner.I see a bunch of discussion around "substantial services".

Hi Chris, I presume getting an attorney is the best option especially since some legal action of some kind will be needed.

Can we avoid any legal litigation here?

Can parents legally force me to attend a university?

. --- If you close on the property in November and immediately send the 30-Day, you LEGALLY have to wait until January 1 to file a landlord-tenant case to regain possession is the tenants have not vacated.4) Your rent losses will be November, December, January, February and probably March if the tenants choose not to pay and you have to evict.--- Make sure seller at least collects & prorates November rent to you!