Thats all I shoot with is canon. Im hooked and their glass is amazing. If you do any protraits a prime lens I would recommend is the 50mm 1.8 , F Stop from 1.8-22 talk about blurring the background this is it. I really like shooting with it.
I have the lens you refer to also. It is a great lens for indoor. The 100-400 is an expensive lense. The 500 to 600mm lens are known as "bird lens" because thats what people take in the wild and a lot of zoo photographers use them for up close shots. Hard core bird photographers have 10,000 in just a lens and body.
A website I frequent is http://photography-on-the.net/forum/ its a canon sponsored website. They guys that shoot for FHM, Playboy, Style, and all those other magazines are on there. If you want to learn some stuff thats where to go. I will say I am a very good photographer and do a lot of it. But I have learned many new techniques and interesting facts from that site.