So pick a market that is easily and readily accessible to you.

The challenge with using a paid option is expecting one person to have all the knowledge you need to succeed unless that person is giving you access to their board. 

This market is not always available in the MLS, so making it more difficult.A commercial lending is possible even with SFH, that will depend on your lender and the access to commercial programs, it will all depend on the situation.  

Additional things to consider: where is the breaker box and do both units have access to it if needed?

Do you use anything for remote access for maintenance? 

They can provide personalized advice and may have access to loan programs that suit your needs.

Access to Larger Loan Amounts: Cross collateralization allows borrowers to leverage multiple properties, which can lead to a higher overall loan amount than what might be possible with a single property.2.

Pretty solid points here, I would also like to add refinancing with a non-traditional DSCR based loan can assist with getting access to cash quickly as there are many lenders that have a lower seasoning requirement. 

You may have to sell the whole property to access the funds in the IRA or 401k when you retire and for required minimum distributions. 

This information is public record, and anyone can access it.