The following link (shared on a GameFAQs topic by Betwixt00 and toki_suzukiko) lists the events available in the Diva Room. The page is translated through Google translate, so some sections may seem vague or awkward to understand, but it gives an idea of what’s what.
Certain items have multiple events, so just keep gifting or activating them.
To those who feel like they can’t import the games because they don’t know any Japanese, or who are struggling to navigate around in-game, please refer to the Project DIVA Wiki.
It has translations and images for the games, which will help you understand the menus etc. I used this back when I played PDf.
Info on PDf2nd is still scarce at the moment, but hopefully those who run/manage the content will add more soon.
Just to add, please note that the wiki is not run nor added to by the two of us running this blog (digitalAlchemist and I). -★üxt