I've sometimes wondered if a 70-200 mm f/2.8 II with 2x extender would be better in a kit than the 100-400 L, so I am not trying to dissuade you from considering it, but it is also a lot more money. But, I think this may be more the case for FF than for cropped sensor bodies. I can say is that for a couple of years my primary kit was the 7D, EFS 15-85, and 100-400L. It worked great and allowed me to photograph a little of everything primarily with two lenses.

As you are new to photography, a suggestion would be to buy a used 100-400L. If you don't like it you can turn around and sell it for probably very close to the same price you bought it for. Places to buy used include craigslist, ebay and fredmiranda.com (and occasionally here).