My best advice without knowing what you want to do would be to attend some of the local meet ups and to reach out to a local real estate broker at one of the big name brokerages to discuss whether this is a viable path.

I work with a really great brokerage, KW, and they having a global presence have affiliated market boards for members only to utilize, so if you belong to or work with a major brokerage check with them and see if they have anything similar.

I believe Dual Agency is much more prevalent in Business Brokerage.

Looking to see what people's experience and view is of each discount brokerage.

Should I file with a brokerage and try working part-time as an agent?

If I can make it work, it would save me a substantial amount of taxes.I would then plan on taking those funds (profit from the flip) and either (a) investing it in other self directed eligible assets (RE, LLC interests, etc.) or (b) transferring it back to a traditional brokerage firm and to simply invest it in equities.  

Was your property manager a licensed real estate brokerage?

As a licensed real estate broker "agent".2.

Tell me more about BRRRR and taking commissions as the broker/agent on both sides of all new purchases.

There are large brokerages that operate multi state.