Good evening Dominique and welcome to the Events Calendar forum!
Thank you for your interest in our products.
We’ll be glad to answer your questions.
One particular client would like to have a ticketing system on top of the WooCommerce.
This can be achieved via our Event Tickets Plus premium add-on: https://theeventscalendar.com/product/wordpress-event-tickets-plus/
Can you activate the plugin for only one site of a WordPress Multisite?
Yes you can.
Just grab a copy of a personal license and install the plugin only on that one site.
Although this is totally cool to do, the caveat is that using a personal license on a multisite install will remove the ability to do updates automatically via wp-admin.
In other words, all updates will have to be performed manually on your end.
Thank you for your suggestion of emails as a ticketing solution.
We might do that at a later point in time, but so far we find that the forum approach provides greater value for people to find out answers to similar questions.
The good news is that our customers also get the ability to do private forum posts.
Let me know how that goes.
Best regards,
Geoff B.