1/ Multiplayer games can be built in C2, but are pretty complicated to put online and HTML5 isn't fit for synchronous multiplayer at the moment.
You can find more informations about this in the section "Multiplayer/Networking" in the How do I FAQ (link in my signature).
But interfacing your game for facebook is partly handled in C2 already, be sure to check the tutorial how to make facebook game and the facebook plugin manual entry.
2/ To make graphical sprites you can either use the built in image editor or some external software like photoshop, the Gimp, paint.net, ...
The logical object itself you do it using C2's event and plugin/behavior system.
For maps, you can import rooms from gamemaker or even from Tiled editor map thanks to a third part plugin.
3/ No. In the free version though, there is a limit of 100 events to use in your whole project, and you can only use 4 layers per layout.
Those limitations may or may not impact on the number of levels though it depends on how you implement your game.
4/ I'm not sure to understand this question.
5/ RPGs can be made in C2 using C2's event system. You can use third part JS plugins to help with tasks, but C2 in itself is enough.
Though it's a complex task that needs to understand and know your way in C2.
I'd first strongly recommend you to check several tutorials first (there are some that directly treat RPG).
Be sure to go through the article "New to Construct: Where to start" in my signature and follow the diverse documentation linked in it.
It should help you get a better grasp on how to work with Construct 2.
Consider it as a programming language in its own right, fiddle a bit with it and get conquered.
Welcome to C2 and the community.