I don't see any reason you'd run into problems with your described setup as long as you script it right. Some of the things, such as NPCs having different 'states' for each player, are not necessarily built into the language, but are trivial to write yourself. You can do almost anything you want to with the interface.
There are limits on the number of NPCs you can create, but the limit is quite large (I don't have the exact numbers) and generally won't be a problem.
There are lots of people in the scripting forums who will be able (and willing) to provide specific details on best practices for implementing these ideas in Graal.
At the moment, the only way to try Graal server development is with the offline level editor (or
Gonstruct), but you won't be able to script with it. You can probably find somebody willing to let you play with NC on their server if you ask nicely enough.