I’d start with lenders who specifically market themselves as “IRA non-recourse loan” providers.My view on it, it’s a solid tool for unlocking 401k/IRA money for real estate, but the costs and restrictions are real.

They usually have restrictions on how much the voucher will pay based off the amount of bedrooms.

Check the HOA/CC&R to see if there are any restrictions on renting in the development or any restrictions on investors buying.

Most agents are not restricted to the city areas and will go out if needed.

What's up gang! Austin City Council just passed a fresh set of STR regulations. A few shifts: tighter rules around licenses, new limits in multifamily buildings, and stricter enforcement timelines.
This doesn't hurt ...

My experience (not restricted to ADUs) is if the units are detached, it is a policy per detached unit and if they are attached it is one policy covering all attached units.  

This heavily restricts how I can use them.

Are there restrictions because it’s FHA?

Warrenton & Gearhart - Several prime luxury HOA communities that currently allow nightly vacation rentals have either drafted or are considering rules that restrict the density or saturation or outright usage of new rentals (existing would be 'grandfathered.') 

Again, with every deal, a different set of terms and conditions apply but the overall theme is that TIC's are no debt, a little less risky in most peoples view but restrict your ability to leverage the asset.