Agree with those who recommend Syl Arena's book. Don't buy any flash yet. Get his book and read it, visit his site watch his tutorials on the 600EX RT and ST-E3-RT so you are familiar with Canon's RT system. If you are not sure if or what, then there is no need to rush into anything just yet.
Then you can decide if a single 430EX II is sufficient, or if it's worth investing in Canon's RT system, or if a cheaper 3rd party unit will suffice.