But from what I understand, delivering the place vacant wouldn't be possible, correct?

Who is choosing, providing, and delivering the materials?

It takes him a day or two to respond to emails/texts and it seems he over promises and under delivers...

If you can find a bank that will allow you to buy three or four houses with that money, you'll produce decent cashflow immediately and have anywhere between $750,000 and $1.25 million assets under management.If I were in the driver's seat for this one, the only tweak I'd make on that plan would be to purchase the largest Whole Life Insurance policy I could afford.

Typically your PSA will have wording similar to " Seller shall deliver Purchaser possession of the Property free and clear of any tenants, occupants and/or rights of possession, excepting the current leases.......". 

If the contract isn’t signed, maybe stall it out three weeks where he doesnt come to your property or deliver any materials and you have proof, until he can’t file a lien anymore.

It is taking months to get windows delivered. 

Have a process server deliver notice to vacate and have it translated into their native language.

The prospective tenant sends a copy of their driver's license and the property manager gives them the code to the lockbox so they can walk themselves through.

@Shelby LeBlancIt may make more sense to have the Seller deliver the property vacant at closing if they are open to that.