Most require 25% down, but there are some really good niche programs out there nowadays. 

Most portfolio lending programs that I have run across will only refi 65-75% of FMV as determined by an appraisal.

Mortgage brokers are familiar with a variety of different loan programs and sometimes have connections to private lenders as well.

PML and HML are two different types of loans/lending programs.

If you are going to call realtors, call them, introduce yourself, tell them you want to send them some information on loan programs that may help them increase business.

They are selling programs and they are telling you that you can do it if you only had the right guidance.

Any recommendations on best way to obtain a commercial mortgage similar to B2R programs?

I'm not sure if the new RRIO program covers this on the inspection, but I do know they look for illegal rental units (which the ADU would likely be considered if you don't live on property).  

As I'm looking to house hack and would love to take advantage of loan programs for first time home owners.

I've definitely seen the land academy system as well as Seth and Marks programs.