You will want three-years of taxes.
-Verifiy occupancy, including economic occupancy (who is actually paying).
-Verify how many people are behind on payments.
-Make sure all late payers are paid up by closing or lien saled.
-Require all "empty" units be cleaned out and truly empty. No trash/junk left on premises.
-Verify who has paid security deposits and get those when transaction takes place.
-Verify how much each customer is actually paying. Many times the amounts are different than the listed price.
-Note deferred maintenance (roofs, doors, springs, latches, seal coating, etc.)
-Get phone, email, website, social media passwords and account information transferred to you in the transaction.
-Get all equipment, locks, keys, brooms, codes, etc. transferred to you.
-Implement new leases with customers ASAP and make sure the terms are up-to-date. Your state storage association may have a sample lease for you to use.
-Base your desired cap rate on other comparible properties, size and location.
I got an SBA loan for mine and had to put 20% down. It took a while but worked out well.
Good luck!