Hi there!
You can read more about how the Events Calendar handles REST API endpoints here: https://theeventscalendar.com/knowledgebase/introduction-events-calendar-rest-api/
When creating scheduled imports in Aggregator, you can set a category for all events that come in through that feed.
You cannot pull in only events that have a certain category at the source, but you can import events based on keywords, date and location. So if the category is included in the title or description, this may work.

The setting for how far in the future events are imported is a global setting, and applies to all imports. There is not a way to set different values for individual calendars.
Hope that helps! Let me know if you have any other questions about this.
Thanks,
Sky