I have 2 options:- finance the construction pre-selling the apt, and take my profits (expected to be around 700K pre-tax); or- finance the construction with a 6-7%/year loan (collateral = my house), keep the 10 units, and once the building is completed in 24 months, rent them for circa 180K/ year gross.

Staging your house well can help you attract more attention from buyers, which ultimately helps it sell faster and maybe for a higher price than an unstaged home (see visual):What Are My Staging Options?

Paid platforms often offer additional features like market analytics, off-market property leads, and filters for investor-specific criteria, giving them a leg up over free options.

While I have a fantastic rate, the co-owner's giving me the option to refinance or he'll force a sale.

As ground-up ADU builds gain popularity I hope we see some affordable options, like modular, but from what I'm seeing now the ROI just wouldn't be there.I'm trying to help spread the word about this law and compile as much information as possible so I can help investors capitalize on it.

Best option would be to separately meter the property 2.

If that doesn’t work, then on to another option.

Just make sure the town is ok with the land being zoned for multi-units, and look into construction costs, financing options, and permits ahead of time.

@Michael Klinger  As others posted, SoFi and Discover personal loans are good options and I've used them in the past.  2-3 business days from application to funds in my checking account. 

Are there any options for lower down payment loans in general or even for college students?