Do I NEED fans inside my case?

Unless you've got other plans, I would get a 120mm for the rear to act as an exhaust. That Phenom II will still kick out a lot of heat under load and a fan blowing into the case just won't be enough, you'll need an exhaust fan to remove that hot air from the case.

personally i would at least put a rear or top exhaust fan in

especially if you have high ambient temperatures

though you could always try it with only the front intake to see how hot it gets--if its ok then fine if not get another 120mm for exhaust

You want one at the back top or top back, yes. Both those parts produce a fair bit of heat.

I would concur that you want to pick up a second fan. It shouldn't be to big of a price increase (~$5 for a basic 120mm fan on newegg).

I have that case and a Phenom II 955 but no GPU. With the Intake fan included and the mesh at the front is enough for my build. But with a GPU the temps will increase a lot, try to get another fan for the side.

Check another cases at the same price, sometimes you find something better.

If you can and want to change the case for better airflow check the Zalman cases, excellent build quality and this two comes with 2 120 mm intake and exhaust fans.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Besides the Z9 is in rebate, and the price of those 2 is pretty similar to a CM Elite 430.
I don't know if you can buy from newegg, but check those cases.

Just move the front intake fan to the top rear spot and you should be good to go.

I have 2 exhaust fans in my case (besides the one in the PSU), 1 top and 1 rear top. I don't have any intake fans, and my temps are as follows:

Core i5 2500 at 3,5Ghz with CM 212 Hyper Evo - Idle/load:

28c/42c

HDDs:

Disk 1: W.D. 1Tb Caviar black: 36c

Disk 2: W.D. Velociraptor 600Gb: 30c

GTX 660 Idle/Load:

32c/58c

Settle with the 1 fan that comes with the case as exhaust for now, and add another one later IMHO.