You can't overclock an i5 3470 and it will run up to 3.6GHz in turbo mode with the stock HSF. You can certainly buy a Cooler Master 212+ if you can afford it because the CPU will run cooler, but it definitely isn't required.
I already have a 212+ but i just may want to sell if for other purposes. I also saw videos where people overclocked it to 4GHZ and hear it isn't fully locked :S
It can be overclocked, but not as easily as you could with a K version. It also depends on your motherboard. If you already bought the coooler, then use it.