I do seed and sets.. Seed I scatter sow early Jan into large trays and heated propagator till they are a couple of inches high. Then just open in the conservatory then into the greenhouse about mid-end Feb'ish and leave till they are at least 2-3mm in diameter before planting out in Spring - normally mid March'ish. My early sets I plant into modules in mid Feb and plant out mid March when i also plant the rest of the sets as a normal main crop.
You can also do individual modules with 2-4 seeds each in Jan/Feb then just leave the strongest one after they are about 4" high. Then plant out in March.