It can be as simple as a form letter in the mail or attached to the door. 

My main lease prohibits washer/dryers in the units unless we give written permission (which would be the addendum).Here's what mine looks like:THIS ADDENDUM IS HEREBY MADE A PART OF THAT CERTAIN LEASE AGREEMENT EXECUTED ON _______________ BETWEEN _______________________ (“Tenant”) AND ______________________ (“Landlord”) Rental Unit Address:This agreement serves as consent from the Landlord to permit Tenant(s) to attach and use a clothes washer and/or dryer within the aforementioned rental unit under the following conditions:Any damage to the Premises caused by water originating from the washer and/or its connecting hoses will repaired by the Landlord at the undersigned Tenant(s) expense.Tenant agrees to regularly maintain and clean lint/debris from the dryer unit itself as well as attached ducting.

Some accounting software (like QBO) let you attach documents in the transaction. 

Did not attach the link.

They have all said that they don't add any value for an owned system like mine, which seems wrong, as there is a lot of expensive equipment attached to our property. 

If it really is 8 units it will not be good, there will probably be a ton of deferred maintenance so the low purchase price comes with strings attached that you will have to fix a lot of things to avoid being a slumlord.

After a few years he'll lose the emotional attachment to the properties since he'll only have been getting payments for mortgage and you might be able to discount the note at that time.  

Assuming the lender is unwilling to transfer the deed, or has a penalty attached to transferring deed. 

PM is fine if you don't want global sharing.I've been using Airtable (which is excel like but let's me attach receipts to rows).  

We are currently negotiating on three properties and will hopefully have a couple under contract soon.Also, I have to add...when I left their office to drive back to the airport, my rental car had a flat tire and without even hesitating, both Joel and Scott jumped in and changed my tire in record time (photo attached).