Hi Sven,
Thanks for getting in touch! 🙂 As it turns out, we do have exactly such an option for logged-in users to view their RSVPs and/or purchased tickets on your site. You can learn more about this feature and how to implement it on our Knowledgebase here!
Regarding your second question, I’m afraid that we don’t have a built-in option for one-click ordering at this time. However, if a logged-in user adds a paid ticket to their cart, their purchase information (such as name and address) will be automatically filled in when they proceed to checkout, though this doesn’t apply to additional attendee information fields (which are filled in before checkout).
I hope that helps to answer your questions here! Thanks again, and let us know if there’s anything else that we can assist with!