Hi J,
Some great questions there.
I just can’t figure out how to give access to the event managers to check-in users for only their event. I don’t want to give them access to all of WP admin just one event.
Granting admin access to users but restricting them to only a subset of posts in a specific post type (ie, their events plus the matching attendee lists) is possible but would be a fairly advanced customization and I’m afraid we can’t assist with that here on the support forums.
Also, can we have option to automatically send attendee list by email either after END SALE time or XX hours before event. I don’t want to have to remember to do it every time 
That’s a really interesting idea and could be a useful feature for sure – right now though, short of writing a set of snippets to handle this, there is no built-in mechanism that will do this.
I definitely see the utility of it, though. If you want to, please do post this on our UserVoice channel – which is where we gather feature requests – and similarly so for the first item.
A benefit to posting feature requests in that way is that others can comment on and upvote your ideas, giving us a much better sense of how much demand there might be for this (though, of course, we’re open to any good ideas – it’s not just a question of popularity).
Do remember to search for similar existing ideas which you in turn might upvote!
Thanks 🙂