my thought was 6 calla lilies, even if they are small, are already going to be crowded in a pot that's a foot in diameter. I'm usually guilty of crowding, and 3 would be really crowded and they will stretch up and likely topple over.

Other than that, I can't be of much help. I'm in TX and we have to plant callas in bright shade next to a drippy faucet...grins

I agree with Cynthia on the pot size and part shade for Callas. Have you tried Hymenocallis? I like Sulpher Queen, a bright yellow. They should be available now. Al

Crinums are wonderful summer bulbs, but one would need a bigger pot: at least 18" in diameter.

Zephyranthes (rain lilies) might grow well in a pot that size.