Rather than carrying a 50% note, you will have a promissory note tied to a cash loan to the buyer.  

If it is tied to the home, you have a few options:1) include electricity in the rent (down side with that is tenants may be less diligent with electricity use and increase the bill)2) have the tenant pay it and include a copy of the statement every 1-2 months to show that it is paid in full.3) have the bill in your name and send a copy to the tenant each month (or whatever the billing cycle is) and they can add the balance to their rent each month. 

ADUs have one major flaw that you just can't ignore, and that's the owner occupancy provision it has tied to it.

You need a stronger pull here.

Tied to an SEC shelf registration where the issuing firm says they will issue debt over a period of time in the form of medium term notes.Depending on what role you want to play you may need to be licensed or otherwise regulated.MTNs are mostly for companies that want to borrow funds for projects, working capital, etc.

Im effectively tying up 25% equity but getting cash flow YoY wothkut really ever needing to own the asset.

This may be an even stronger argument in your favor.

You'd be tying up a lot of money on one property. 

Within 1 year we were publishing in booking and a few smaller channels and tied in to a pricing engine, lock automation, setup a set of great communication workflows, etc.

I would encourage you to see about getting something before you separate as your ability to get a loan should be stronger now - but talking to a great lender will give you the ultimate answer you'll need about that.