Q - How many missions are there?
A - There's ten you really play through to get all the rewards. Which area you get and what you do varies. I'd say there's maybe two dozen or so.
From what I gather there is nothing really interesting after the tenth playthrough. But Nintendo said there was some reward for playing everyday, whatever that means. I just tried playing after midnight to see if anything new came up, but it doesn't seem to do anything. Mega Glalie seems to be the main attraction here. I am not sure but I think I've seen all the major stuff in this demo. - Source
Marriland's page talks about 10 adventure/missions and they already have a list of items you can get in each mission. You can see that here.
Hope this helps.