Email and SMS Event Reminders

Disclaimer: I haven't done this sort of thing before in Braze in a proper integrated/automated way.

I'd start with the basics, what do you want to achieve? Just reminders? Sending other 'you might be interested in' type events? Is it possible/likely that there will be folk registered for multiple events? multiple events on the same day (and if so, how do you want to handle that?

Then some data planning to support those goals...
Who is your 'user' in Braze - presumably you have some sort of identity model already - where each person has an email address (think about uniqueness here, Braze doesn't force you to make emails unique)
What is an event in your case? Individual instances, or can they be recurring?

Then it's 'just' a case of recording which events and when they're happening - depending on how you need things to behave will determine the sort of data structures you'll end up with.

I'd hope that you have some sort of system that knows about all the events/registrations and you can get that data into Braze in whatever shape you need.

This isn't all terribly difficult, but is worth taking time over to make sure it's done well. Would be happy to help with that sort of thing (feel free to DM me).