I currently have a sfh with a detached garage that I plan on converting into an ADU.

Quote from @Anshuman Thakur: Can someone please shed some light on how- convert 401k to SD IRA- how to use SDIRA to buy properties- how much down payment is typically required if we are using SDiRA to only fund downpayment on a multifamily CRE, and which banks typically work with SDIRAs- how does LLC structure- property management and cash flow work in this situation?

Look for adding square footage to property maybe converting an attached garage to living space, or adding a bathroom or bedroom to the units to fetch higher rents. 

This requires careful structuring and compliance with IRS rules.Installment Sales or Buyouts – Instead of distributing properties outright, investors can sell or buy out their respective shares over time, spreading out tax liability and reducing immediate capital gains impact.LLC Restructuring (State-Specific) – Converting the corporation into an LLC taxed as a partnership may allow for a more tax-efficient asset distribution.

Quote from @DR Rearwin: Be aware that if you purchase a property as your principal residence, and later convert it to a rental, the lender may have the option of calling your loan and making you pay it all back immediately, since you have changed the use of the property.I never knew that.

You can qualify for lower down payment loans, and after a year you can move out, keep the same loan terms and convert the unit you vacated into a rental.thank you!

Stay consistent with your calling and sharpen your skills as you continue so that you convert leads at a higher rate.All the best!

A large number of the homes were unofficially converted into duplexes in the 90s/00s (though kept as SF in the official zoning).

Quote from @Colton Bridges: I recently bought a duplex that I plan to convert to a fourplex.

I'm surprised someone verbally told you you can convert back to a duplex and didn't tell you that you must get permits.from what you are describing it seems the town gave you a hard time because you didn't get permits, I don't know that you have any legal standing to go after the town,  again, I am not an attorney