Congrats on discovering the One Note Samba! Well done! That was one of my favourite lessons, I loved that LH pattern. I agree that this is an excellent way to start with hand independence. Funny enough I was going to suggest gradually adding some notes of the blues scale, but WieWie beat me to it. Perhaps not all notes immediately, but just C and Eb, randomly.
I am only 0.0003 steps ahead of you when it comes to improvisation, but I found that my ears quickly tell me which combinations sound groovy, and which to avoid. So sometimes you may find that Eb is not a great sound for the chord, but then you can slide it quickly to E. That way you will find your own unique sound quickly - I can't wait to hear the next iteration of your skills!
I also enjoy this background sound a lot! Sounds very rich!