I'm particularly passionate about potential flips and BRRR’s, even outside of the DMV area.

The first rule of gambling is that no single loss can wipe you out.

If I sell a single family house for $1 million which has a mortgage of $100k, can I do the following: I buy a single family house property using 1031 exchange for $1 million and get a mortgage of $700k .

Maybe what I'm looking for doesn't exist.. but just consider that even if you tell me a couple of places that are at least open to STRs you'd be helping. 

It just won't happen-  low ARVs even if you do renovate.

But financing even with 50% down seems to violate the 50% rule.

This was completely my fault due to lack of due diligence but not having the ADU dosent kill the deal it cash flows great and I can always use the ADU as a single guest bedroom to the original rental but would be better if rented separately

It was originally a single family converted into a 4 so it just doesn't work well for design. 

As you are probably aware FHA rules state "FHA’s single family programs are limited to owner-occupied principal residences only."

You can even get exposure to C class in some suburbs.