1.) Currently, there are three Role plays.
A.)
The character lounge, which is informal, doesn't follow a specific plot, and is just a chance to test character's out.
B.)
The show re-enacted, which is currently in Beast Wars Part II. It follows the script pretty closely, but may become more loose, and either way, the integration of original characters make it's more interesting than simply re-writing the script online.
C.)
O.C. Episode #1, which is actually an in season (coordinating with the show re-enactment role play) introduction of the adventures of many Maximals and Predacons who wake up on Earth but have yet to meet up with the Darksyde of Axalon. Unfortunately, (for your tastes), this involves no Cannon characters, unless there's a tie in at the end like "Hey Boss Monkey- who da heck are they?", that sort of thing. But if you wanted to join with an original character, I think Alak said that anyone can join at any point, so... free admission.
As for joining as a cannon, you already took a step by auditioning for multiple characters, so I suppose it's a matter of hearing back from Optimal Optimus Primal, and perhaps whoever is playing the characters right now. Of course, they are meant to be played temporarily (those which are listed in the "Characters for Sale" thread).
2.) Looks like I kinda' answered that, but maybe not to the fullest extent. Essentially, there are some roles which have been filled since the
original roster Tor, for example, is still playing Waspinator, and will continue doing so for as long as she is willing and able. But some people auditioned, got the parts, but then became understandably busy (such as Jagna and Razor One), and in so doing left their parts open (these are the ones in the Characters for Sale thread). As far as I can tell, anything in the characters for sale thread is up for grabs, given approval by Optimal Optimus Primal of course, and general consensus by everyone else (which shouldn't be that hard to come by).
3.) Hmm... I don't what happened to Beast wars Part II specifically, but the first episode saw far bigger pauses than the 4 day one than the second episode is (which is a large reason why characters are up for grabs. We want their roles fulfilled so the role play can proceed smoothly). I'm sure it'll be back on it's feet. I believe O.C. episode #1 is still going, and the character lounge might be kinda' sluggish. But you can certainly join it if you want. After all, new participation probably would be a good way to kickstart that.
As for Terrorsaur and Megatron, maybe you could pm Optimal Optimus Primal directly and work out all the details about if you have the parts, if you can start using them, etc.
I understand... you are, after all, a predacon.
[img]http://www.bwint.net/memberfanclubterrorsaur.jpg[/img] [img]http://www.bwint.net/bannersbfanclub2.jpg[/img]
This egg has a Predacon symbol, yess. 
I haven't had time to review the episode lately and figure out how to approach the next step in the game, but I'll start working on it right now so people start posting again. 
).