If you get full-size bulbs, 1 per pot should be enough, 3 if you don't really want to see the pots. I'm not sure there will be enough room for Impatiens because if you get fat, vigorous bulbs, they'll form a solid dome-shape from the soil level.
I love the thought, some pink and salmon Impatiens next to CW's would be beautiful. Maybe lean the Impatiens toward the rim a bit?
Do you want to consider pairing the CWs with something more trailing? One of the tiny-leaved Coleus, some kind of Plectranthus? Probably depends on the site of the pots. You know I love about any kind of combo, but would take some pondering to decide on a companion for potted Cal.
There are some great pics of CW here.
Fancy-Leaf Caladium (Caladium 'Carolyn Wharton')