My plugin (amr-events) will work with existing categories (and you can choose standard posts or custom post types) There is also a way to convert any existing posts into ‘event’ posts in case there is alot of content already built into a post for an event.
It is a paid plugin (the free version at test) works with ics files, They share the same recurring and listing engine for event data. See the rating at wp.
You can test out amr-events out for free at test.icalvents.com