Because I haven't gotten into a single fighting game I have ever purchased. That's not to say I haven't had fun with them, but I rarely practice because of how difficult they are (combos and that kind of stuff). And yeah, I got a little turned off by the combo videos.
This is probably the first fighting game I've been looking forward to due to previous interest in the series.
Well take it slow at first, remember that there is auto combo for you to start off with to get a feel for the game. Eventually you will have to stop using it as your crutch but that depends on how much time you'd like to spend on the game on it for multiplayer vs the story mode. There's plenty of people here who will play both casually and competitively, so no matter what you should be able to play with people around your skill level and still enjoy it.
Keep in mind that you don't have to become pro at the game, but I imagine most people would like to be at least competent. Think of it like playing DotA, the more time you invest in it the better you'll get and everyone has to start from the bottom.