California building code has a minimum standard for noise transfer between floors which is at least 50 STC (sound transmission like voices, tv, etc) and at least 50 IIC (impact noise, people walking or jumping). 

Zillow.com,  Craigslist,  FB marketplace.Send letters to distressed property owners, probate, divorce, pre foreclosure, code violations etc.

Also, make sure your property is up to code and doesn't have any outstanding liability issues.  

I also know they have talked to Riverside City officials and they were very supportive of the units and were looking at similar city code for ADU's as other cities have adopted that would make the approval process pretty quick and easy for these units, since they are prefab the plans don't change on the design it's only a matter of approving the location of the site you wish to place the unit on. 

For example: "Two Story Single Family Colonial Homes with at least 2100 sq. ft. within a 3 mile radius of the interstate without an HOA with less than $15,000 renovation that $450 cash-flows/month which I can purchase for less than $350,000 in the zip code 22407".Is $420/mth below or over your baseline/worth it/ideal cash-flow per door for your criteria?

I like Notes because once I establish the right partnerships and connections, it seems that all that I'll need is a laptop and a decent internet connection to do business.Bottom line: spend your time learning and networking, go to real estate clubs and network when you're at home to find good business partners, physically check out the areas you want to invest in.Hope this helps....

Here, it can take over 2 weeks for city/county/utility and code violation searches for non recorded liens and these timelines are controlled by the agencies.

You also want to be sure that your kitchen and bath layouts are functional and meet code. 

The main reason for doing this is because we will have "scam tenants" that schedule a showing with a fake identity, income, etc then will try and steal the door code from us when at the showing so they can break into the property after the showing.

I am aware that we also will have to get it up to code for such an operation.