Deposit money should be held by a neutral party like the title company if you are not using a realtor.

I'm interested in popularizing this topic and starting a network of interested parties in any capacity. 

This option comes with $0 doc/origination fee, though I do think there might be some third-party costs of $20 or so.

You should make sure all parties agree to this in writing, just so everyone understands and feels their interests are being protected. 

@Chris Reid Welcome to the party, sorry I'm late to the game.

I know these 3rd party companies can take a hotel given to them by a buyer, reposition it, and then even manage it for you, creating a semi-absentee owner investment.  

If you have a lease, neither you nor the landlord can terminate the tenancy prior to the expiration date of the lease, unless the other party has violated a provision in the lease.

I wouldn't recommend buying partials on notes that aren't 3rd-party serviced.The contract should spell out exactly how many payments you're buying, for how much and the estimated return you should expect (no guarantees).

How will you split the deal to make it beneficial for both parties?

As for analytics on mail sent you will need a third party tracking system.