Sounds like you have a good plan moving forward for your investments and great markets selected for BRRRRs. 

I have done some research on ADUs and have come to conclusion that getting a house near a hospital or good college area with a big yard to add an adu and convert gargae to junior adu would be best.

It is very competitive but if you utilize good resources and think smart you can do really well!!

What criteria do investors use to determine if a seller financed deal is good?

I also live in NY and have invested long distance without scouting the area. 

A relative who does long-distance real estate investing told me that I have to sign the final loan document and the transfer of ownership document in person.

Quote from @Chinku Chinku: Got a townhome in suburb area of Houston for long term rental close to katy mills (<5miles).

@Bryce Jamison As long as the previous owner keeps up with the maintenance of the home and keeps it in good condition, I tend to favor older homes in established neighborhoods.

I think the economy has a number of diverse employment options, lower prices than King County while still being within driving distance.  

Make sure to have some good cleaners, not just one, but a few.