I grow in 3.5" / 9cm pots, except for roots (thing that don't like being transplanted like Parsnips and Sweetcorn I grow in Richy Paper Pots and transplant out whole, carrots I grow in containers).
This gives me a lot of control over the number of plants, at the cost of some fiddling pricking out and potting up / on etc. and as mumofstig recommends I sow for the number that I use in a given period.
I record the number I plant out (at each planting) and then against that whether it was enough, or not, and change the quantity next year. I also record the date of First and Last harvest (actually when it was ready, and when I think it would stand until, if I have harvested the last one before then) to form an idea of how often I need to sow.
Trouble with sowing in a drill, IME, is that they come up when there is a rain shower or similar, so sowing now may give first harvest two weeks earlier than expected, or two weeks later ... sowing in seed trays gives me more control - but folk may just think me too much of a control freak?!!