ID Meeting and upgrade

Dear Community, I am quite new to zoom and would need your help. I created a MeetingID and will have a meeting for a lot of  participants. How can I allow all of them to enter the meeting immediately without clicking on each attendee separately.  And my second question: if I already created an ID and would like to upgrade to a payed version, are all the payed features available to the already created Meeting ID?

Thank you.