1)How to grow an email list? Many creators offer an incentive to join. They are called lead magnets or opt-ins. People are more apt to give their email if they receive something valuable. Check out Newsletter University in the Learn section. https://learn.convertkit.com/courses/newsletters12
2) To determine if subscribers have confirmed go to GROW - SUBSCRIBE - in the Confirmed Subscriber drop-down - Click UNCONFIRMED SUBSCRIBER. This will tell you who has not confirmed their email. If you set that up.
3) I added my email subscribers to my list without having them confirm because I already did that on the previous platform. I downloaded the list and then uploaded to CK. Hope this helps