I can answer some:
Unfortunately no Visionaire games wont run on the web
, there is a Mac version underway and talk about going on to support touch screen handhelds
It doesn't use Flash, but obviously you can use Flash to create character animation and sequences (frame image exports) and AVI movies clips.
You can also make "stuff" happen while animation is running with Visionaire similar to Flash, for example when the timeline hits frame 20, you can make the character move, turn something one etc, then on the last frame do something else.
There's an excellent tutorial by GlenFX which is in the tutorial section, also a Wiki:
http://wiki.visionaire2d.net/index.php?title=Main_Page
I honestly don't know if you could do a multiplayer game.
I used to do flash games and the amount of bandwidth needed is very scary, so I found myself having to consider making AIR apps which kinda defeated the object!