Fractional note sales

[Al Bunch]

Hopefully someone more experienced can help me wrap my head around this.

Unless it makes a difference, my widget in this example will be a stick-built SFR.

Purchase price $10000
Repairs $5000
ARV $25000
10% down $2500
Note $22500 @ 9% for 8 years (pmt: 329.63)
Actual rate of return 28.26%

This is where I start waving my hands around, making wild guesses and hope you just agree with my #'s.
I'd like to sell a portion of this note (let's say 50%) at a 25% discount, so the sale price would be $8437 (yes?).
This entitles the purchaser to $164.82/mo and I'm assuming a 50% portion of the underlying asset, but at what value ($15k (purchase + repairs), $12.5k($15k minus down pmt), or $22.5k (sales price less down pmt)? or does it matter?

I could obviously completely divest myself of the note, but I enjoy mailbox money and if the borrower defaults, I have no problem taking the property back and starting the process all over.

What happens if the borrower defaults? What is my obligation to the purchaser of the other half of the note.

I've got a ton of questions, but I'm hoping this will at least get some attention by the more experienced folks...

Thanks!