Welcome to NGA!
Planting in pots and planting in the garden are two different animals. In the garden, the spacing would be about 18 inches apart. But to make a basket look nice, the plants have to be crowded - maybe 5 or 6 plants in a 13 inch pot. You can start them directly in your pot but in a 6-pack tray might be easier. If you put 2 - 3 seeds in each cell in a 6-pack and had 100% germination, you would have more than plenty. You can pinch out the less vigorous seedlings and keep the ones that show a lot of vitality or special leaf color.
Dichondra seed needs light to germinate. Place the seeds on the soil and press gently but don't bury them.
Daisy