With the Sunday promo do the listings have to be listed and sold only on Sunday?

No, they have to be listed on Sunday but they can sell any time in their first listing cycle for the terms of the promo to apply, eg. if you list them for 30 days they can sell any time in that 30 days.

Does the Sunday Promo automatically come up each Sunday or do I have to search for it somewhere?

It usually shows in your promotions section where it shows the counters for the freebies. Someone usually posts a link for it so watch out in the forums. The link doesn't work for a lot of people because it's supposed to be by invitation only, but it works for some and is always worth trying.