How many iPads do you need for event check in before the line becomes a complaint

Planning check in for a conference with around 300 people and trying to figure out how many iPads we actually need.

The event is spread across a few hours, but everyone apparently has the same arrival time because calendars are decorative now. I was thinking 4 to 6 devices for registration, plus one spare because the first person to spill coffee near the setup will somehow become my problem.

We may also need a couple for badge printing and attendee help, so the number keeps growing every time I remember another job the iPads are supposed to do. For context, we can rent preconfigured devices with delivery and support, which sounds much better than me becoming unpaid IT during check in.

How many iPads do you usually plan for event check in? Appreciate any thoughts