You’re talking specifically a physical premiere event?
In terms of a step and repeat backdrop, if you want it to be branded you’ll need to buy it. However, because those photos are pretty close to the subjects, it doesn’t need to be huge (and may not even need to be that tall!)- I’d find a cheap big poster to hang, then make sure you’ve got a lighting set up and boom- step and repeat! It only needs to look good in-camera, so fake it a lil!
Online ticket sales are pretty easy to find- EventBrite and TicketTailor are ones we’ve used at Stareable that work well and are easy to set up.
Marketing the event you can pretty much use any of the marketing articles on this site for guidance! It’s just a live event instead of an online one.