- Some rich text + images hosted online for the event
- Subscription form to get updates
- Stats about expected attendance
- ??? (this is my first time)
Edit: I don't charge anything for the event, so percentage commission can work.
I was once looking into using nextcloud for an event. I might have had different requirements, though. But it does have something like Google Docs, it has forms you can send, it has a calendar. I don't think it has the ability to do email lists, though. But it does have a privacy-respecting video conferencing thing, which has almost all the features you'd expect. The thing it doesn't have is auto captioning. Or even a way for a stenographer to display manual captions.
Another thing you might try is Mobilizon. It's a fediverse-equipped program for doing events. It can handle rsvps and all that. It can probably handle emailing rsvped folks better than next cloud can.
It doesn't have the whole document suite or video chat, but it seems like it might be better focused on the stuff you're interested in.