As Elon suggests, a trigger_relay with something like an env_shooter will get rid of the door. If you want it to explode place a func_breakble version of your door in the exact same place rendered invisible (additive, 1) and when the scene starts reneder it to solid 255. That along with getting rid of the door should help there.
For the grunts and barneys to start fighting you could just leave it up to their A.I if you wanted. Or you can, on the last script the grunts execute (running into the room) place a script entity just to run to. You could then, from there, make the entity target the barney. And make the barney target the grunts. That should work.
As for the camera, put the camera moving (if you want) by placing path entitys to follow (not path_track, the other one which i can't remember) and put another invisible train following the grunts on its own seperate path from the grunts, make the camaera target the train and that should work. Then'll you'll just need to mould it so that the path that the entity(s) take fits perfectly with the scene.
There, that may help you