What does a good self hosted event ticketing setup actually need?

I've been looking into how people handle event ticketing when they want to keep more of the setup under their own control.

The basic flow seems simple enough: create an event, offer different ticket types, collect attendee details, take payment, and send some kind of confirmation.

But once you go beyond that there are a lot of smaller things to think about Promo codes, limits, custom questions, check ins, refunds, email notifications, and keeping track of all attendees all start adding up. I'm especially curious about what matters for smaller events where yo don't necessarily need a huge system, but still want the booking experience to feel polished.

For anyone running their own ticketing setup, which features have actually ended up being essential?