Hi Simon,
Thanks so much for your interest in our plugins! Related events functionality is included as part of Events Calendar PRO–when viewing any single event page, you’ll see a selected grouping of related events displayed below the main event details. (If you should wish to disable this feature for any reason, you can do so from your plugin settings.)
Users making RSVPs/reservations using Event Tickets or purchasing tickets with Event Tickets Plus can obtain as many RSVPs/tickets as they’d like in a single order. If your users are logged in when RSVPing or buying tickets, they can log in later to view all of their RSVPs/tickets. You can restrict RSVPs/ticket purchases to logged-in users only, as well–this option can be selected on your plugin settings for Event Tickets/Event Tickets Plus.
I hope that helps! If you should have any other questions, please don’t hesitate to let us know. Cheers, and thanks again for stopping by!