I managed to tweak some of the settings and it now sows seeds in just under 3 minutes. I had to figure out a few things which I explain in the youtube video below.

The interesting thing is that different seed sizes work differently - although the vacuum nozzle is rather small, it still has an affinity for larger lettuce seeds and tends to not always work with smaller or rounder seeds.

All in all this project is pretty much ready, if anyone wants info on how to replicate it you can always contact me.