1 - Yes and many have been made.
2 - Yes and there are quite a few tutorials on the site about how to make a multi-player game.
As for the specs, that all depends on how many events you use, how graphically intensive the game is, how many effects you use and generally how big the final result is. In other words, it depends on the same things as any other game (programmed from the ground up or built with any other tool) depends on. Because Construct 2 is originally an html5 tool, the final package is meant to be extremely light weight.
As for the edited question, see the previous paragraph. Remember, Construct is a tool. It can be used to create just about any type of 2D game you can imagine. But, a tool is only as good as the person using it. A person using a tool improperly can always create a bad product no matter how good the tool is.
As for the choice between CC and C2; C2 is far more powerful and has a lot of great features. Not to mention the larger number of platforms it supports. If your question is between the 2, the answer should be a resounding C2. If you are concerned because it was originally created to make html5 games, just take a look at all the export possibilities and you will see, C2 gives you a lot of options now.
Finally, since C2 has a free version, why not give it a try? That may help you make your decision between the 2. The interface isn't that different. At least from what I remember as I haven't used CC for a couple years.
I hope that helps answer your questions and good luck with your project.