Wow, I’m stunned 
I didn’t even know what to use the Custom Data module for. I feel overwhelmed by all the new stuff I can learn from your tutorial 
Thank you so much for sharing these workflows with us!
Would you mind to tell us how you create your tileable flow noise textures? Do you generate them with a tool or software which already makes them tileable or do you edit them by hand (like in Photoshop using the offset filter)?
I personally think that some ink drops or splashes could even improve your effect. I once did a very simple brush stroke effect for a kanji learning mobile game (take a look here). Of course I get that one could decided against such splashes because they give the effect a different feeling - less serious and magical, more cheerful and action-packed.
However if a brush stroke is drawn as fast as yours, I think ink drops would fit, so I just wanted to mention it. Surely the ink drops I made would be way too bulky for your effect, but maybe some subtle drops would look fine 
I’d be happy to see more of your work and possibly more tutorials too 