Most of what you asked can be answered by using the demo (which you have full access to). On the demo you can create events, add outcomes, place wagers on those outcomes, change the event status' and settle the events seeing every bit of frontend functionality available.
Events are specifically designed to handle multiple outcomes, so yes, it works great for listing many individuals (each being an outcome).
Each Event has its own Comments section with basic core xenforo functionality like Likes, Alerts and newsfeeds. Discussion Thread integration will be in the next major version (which is under development right now). You are able to enable/disable both comments and discussion threads per category... ie, you could have a category that only allows comments for events created within it and you could have several with discussion thread integration and some with none.
No on XenAtendo and I am not sure I am going to either. Kinda waiting on Mike and Kier to see what their stance is on a default calendar system for XF.
Winners are sent an Alert and a newsfeed item is published. They can also check their "My Wagers" area for a detailed view of their wagering.
I don't have any User Critera added to the notices system. I MIGHT look into that in the future, but won't look into anything that isn't suggested in the appropriate forum at the support site.
Don't understand your email question about a season.
There are sidebar modules, XenPorta Modules, [bd] widget framework widgets and a simulated node module, plus Newsfeeds that can all drive traffic to an event.
The best thing you can do is mess around with the Demo. The Pre sales thread has a lot of info in it as well as the Sportsbook forums on the Support site.