Picture is not too useful, as there’s a bunch of data points lying on top of one another so one underestimates the total count.

Nice, sounds very cool!

You could perhaps just flash the lights, or if they’re dimmable, turn them a lot down over eg a duration of 20 seconds

In Denmark you pay after the session - I’ve been one place where it’s monthly invoicing, and another where it was payment after each session (by credit card I think)