I have been to Europe many times and most recently traveled to Tuscany for three weeks. You can see some of the photos here - http://www.flickr.com/photos/calevphoto/sets/72157632050781294/
You should be fine with the 70-200/4. I used to own the 70-200/4 IS and now own the 70-200/2.8 II. The 2.8 II is a much better lens, but the difference is really only noticeable for portraits and action shots - not really architecture and your typical European shot, unless you are photographing the Palio like I was.
I did have a 24-105 there and was a bit disappointed with it. On a FF camera it badly vignettes at 24mm. I would highly recommend you look at a different wide lens. The 17-40 is probably the best if you're on a budget, but the 16-35 is a bit nicer.
If you really want some nice shots though I highly recommend that you invest in TS lenses. I took both my TS-E 17 and my TS-E 24 II there and they were the main lenses I used. There is another thread here with my shots from Tuscany taken with those lenses.
Note that a 580EX is mainly for taking portraits of your family. I did take one but only used it a handful of times because you only really need one when the sun is behind the subject. In most cases you can reposition your subject to make the sun work for you.