Close window with middle mouse button in Expose

Not possible via the trackpad as far as I can tell. You can use the arrow keys though.

I'm not familiar with the particulars of your mouse and the associated drives, it probably hasn't been updated for Lion yet, so I wouldn't expect any Mission Control options built in at the moment. The simplest way would be to see if you can have the button assigned to a particular keypress, which you can then assign to Mission Control in the Keyboard Prefs.

If that doesn't work, try Steermouse, it's a 3rd party mouse driver that works with almost every extra mouse you'll find, and gives you some additional features and flexibility.