Although selling beats online could use an entire comprehensive guide, this is a great post and you nailed it.
I shall not go in on each and every point you made but emphasize the two most important promotion techniques there are.
These are:
1. Offering free beats. I do it myself (
https://omnibeats.com/free-beats. People search for that term in google & youtube all the time.
This will get you traffic to your beats website without even trying!
2. Social media. You mentioned Fb & Twitter, but if you are in the beatselling business, Youtube is the way to go. Basically, 2 ways you can go. You can become a "type beat" poster or a more descriptive poster "hard aggressive trap beat". However, there are many searches for both ways and you will get hits. Make sure to put your links in the video's description!
Personally, Im a "type beat" - poster. Check out my Youtube channel if interested:
https://www.youtube.com/channel/UCUPAqIRWVM8Y56fUru6X5zg and hit me up if you have any questions. Id be glad to help
any producer that is on the come up. Good luck!