Hello. I also thinking of my roller blinds automation and i was found this on thingiverse https://www.thingiverse.com/thing:2392856
Its very cheap project for 5-10€/window. With 28BYJ-48 stepper motor you at least need 9v psu, it's even better with 12v.
I also saw, that someone was already discusing in mysensors forum about how to start this motor and there is a code. Of course if you want to use percentage for open blinds, you should modify code and add some typen of encoder on mechanics. https://forum.mysensors.org/topic/3394/curtain-control-node/31