They need a fairly deep pot as they make long roots. The large size yogurt pots are about the right size - if you use actual yog pots remember to make a drainage hole in the bottom - use a hot metal skewer of similar. It is usual to put two seeds to a pot and choose the stronger one to grow on, but I am too mean to waste seed! But you could even possibly sow them outside now as long as you keep them watered - many people sow indoors as early as December or January. Sow more than you need, because if you have my luck not all of them will be good growers, and there is often a small accident as well! If you pinch out the growing tip they will branch out lower down and you will get more flowers.

Are you growing them in containers or in the ground?
At this time of year you can sow them direct where they are to grow. Allow 8" between plants. So if it's a container you will be growing them in it'll need to be pretty big, at least 12" deep.
If you want to grow them in pots before planting out then to have the best chance of getting reasonable plants i'd sow a couple of seeds in a 3" pot, then choose the strongest plant to grow on. That'll save messing around with untangling roots when planting out.
For future years, you need to sow the seeds a lot earlier ( February time)