Where to get estoppel:  Title company, lawyer handling the close, google it, plenty right here on BP as well, your agent handling the close - lots of options for you.I would never ask the seller to sign a new lease as they are not you. 

Are there companies out there who can handle the furnishing, monthly cleaning, maintenance of the unit?

For someone that is absolutely 100% getting into this game with a long term goal to grow Grow GROW, how would you all handle this?

Does anyone know any title companies in Arizona that handle wholesale transactions?

I can see that since most residential lenders wouldn't be handling something as complex of a financial situation as your investor's. 

Big mistake in not getting a property manager- this one is too big for us to handle.

I'd be surprised if you couldn't connect with a retiree looking for a few extra bucks to handle what you need handled and check up on the cleaning crew for you.

Since you do not own the property yet and are just gathering information, most likely they will not spend hours on writing a bid for free, and most good contractors have more work than they can handle right now.

I've handled title claims in Florida where after the property had been sold, the Assessor became aware the Sellers had been claiming a homestead exemption to reduce the property taxes, without meeting the requirements for the exemption. 

Check with your agent to see how your Insurance carrier will handle it.