There should a special BPM Timer, where you can set the BPM you want and then every beat it will be ON for half a beat.
Rather than having specific gates for each note, I would suggest having a specific gate for each instrument, so that you can just wrench the Piano gate for example and set the note there. Makes it easier and cheaper to experiment.
Admins or people who design items could make a small piano, when you wrench it you could put a note but not play like in real piano but put a note by yourself like in FL Studio.
like this, you could add every note by your self, and also in up there could be a BPM - you could choose bpm you want to be.
also you can wrench piano to lever and click on lever and piano would play your melody.
Sorry I am bad at drawing with Pixels lol but I hope you got my point