Answer: When starting chives, one could use just a seed or two but that would mean waiting several seasons for a strong clump of chives to form. You might try a dozen seeds spread out a bit in the pot to make a nice clump sooner. The clumps can be divided later to make additional plants.
Parsley can also be sown with just a few seeds per pot, however the germination rate of parsley seed tends to be a bit low so at a minimum I would suggest about half a dozen seeds to ensure a better start.
With some experimentation you will see what yields the right amount according to your definition of thick and thin.
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