I think the 600EX-RT is a ridiculous flash choice for a beginner.For the price, assuming OP wanted to go older technology, the 580EX II is a superior choice over the 430EX II for power, guide number, flexibility, master/slave option.
I do paid portrait/wedding work with a 430EX II and two Yongnuo YN560 manual flashes, all of which cost me a total of $300. I also have a set of Phottix Strato II radio triggers but I find in a lot of situations I don't even need them because the YN560s have a reliable and very sensitive optical slave.
If you need a first flash to go with your T3i, the Canon 430EX II is the way to go. It's great because the T3i has an on-board master that can control the 430EX II in TTL mode! That is all you need to get started.
Then head on over to strobist.com and learn how to REALLY use flash. Once you decide it's time for some more flashes, pick up a couple manual flashes and some 3rd party radio triggers (the Phottix Strato IIs are awesome for manual work!) All of this for much less than the cost of a 600EX-RT and the ST-E3. If you REALLY need TTL (you don't) then Yongnuo has great TTL-capable radio trigger set and flashes as well (YN622 trigger for under $100 and the YN568 flash for under $200).
Also if you use the Phottix Strato's and I had them initially and they do work wonderfully for manual flash, if you're going to suggest an upgrade to them, why not the Phottix Odin? They are superior to Yongnuo triggers all day long and I find the TTL in the Odins to work seamlessly with my Canon cameras. The Yongnuo triggers are sketchy at best if he wants to get long service out of them imho...