In order:
yes
yes, and OMG indeed. Cue Chao. Working with Negi by working against him. Though....maybe....
[spoiler]maybe she wants Asuna's power to be used. And Mundus Magicus brought to Mars. I don't really have many ideas on this part yet. Or what exactly would happen if the group from back then (aka Tertius) succeeded.[/spoiler]
Yes (and hilarious)
Actually, I think he's serious. Primarily because of what you mentioned. [spoiler]I mean, they have heavy hints as to it being true in previous chapters, to the point of it being almost official, and then there's that one dude who did confirm it, though he is not to be fully trusted. Of course, this could all be leading up to a major twist on the order of Al being his mom or something. Which would actually fit, as most people would think that it WAS her, and only a select few would know Al was posing as her.[/spoiler] Also...
[spoiler]Negi's "sister" is actually his mother/Asuna's sister. Near the begining when he did the whole show Asuna his memories of 6 years ago thing, Negi's sister (who's name escapes me atm) says in response to Negi asking if she's ever been rescued by Nagi: "That's a secret!". I think there's something in that.[/spoiler]
And yes. It is odd, too.