Hi Britta!
Thanks for reaching out to us!
Unfortunately, we cannot create custom licenses for a specific number of installations.
However, an Event Aggregator license already includes multisite support for up to 10 sites. So, if you need support for additional sites, then you can purchase additional licenses with each license counting for 10 more sites.
The limitation in the number of imports is for every import run, regardless of the site the import is run from. So, if you have 10 sites that are running with the same 100 imports license key, and each of them have 10 imports run per day, this means it will count as 100 imports, thus reaching the import limit.
You can learn more about the import limit in the following article > https://theeventscalendar.com/knowledgebase/event-aggregators-import-limits-work/
I hope that helps! Let me know if any follow up questions.
Best,
Victor