For quiet cooling:

Never buy smaller than 12 cm fans

If your fans cannot be plugged into the mobo, make sure on 12v (MOSFET connector) they are rated to not spin at high RPMs. For example, Cooler Master silent fans spin at 1200 RPM on 12v, which is quiet enough for me, with decent airflow ( decent airflow since I have 3 intake fans and 3 exhaust fans). Otherwise, you have to buy or mod your own 5 or 7 volt MOSFET connectors. Generally for cooler master silent fans, 2000 rpm is audible, and 700 is too slow (i tested using the mobo speed controller) so 1200 RPM hits the sweet spot for me.

Having fan speed regulators will really remove the major headache of noise vs performance. Then you can increase or lower an speeds as and when you need performance, or silence. They may cost quite a bit, but it's a good investment, if you don't mind how they look (most of the affordable ones are ugly and do not fit my casing's look, so I didn't get one)

Noise can also be caused by vibrations, so your mounting process should be considered as well. A rated silent fan won't be so silent if it's only mounted using cable-ties to a CD-ROM bay grill.
As Doom said, If you're not overclocking though, then don't bother with too many fans. your pc should function just fine. Adding fans = more dust = more maintenance required. Go for Prod's suggestion of 1 front intake and one rear exhaust should be sufficient.

I assume you mean the 331, can't find any 311. haha! Well, yes there are side intake vents. I call them intakes because my previous casing had similar vents, and with my setup and mobo design, you can feel air being sucked in the side and not expelled. The lower vent however, might depend on your graphic card. For example, my 8800 gts 512 is a dual slot card, which sucks air from the back end of the card ( the end that faces the HDD racks) and expells air out at the dvi ports (the back of the pc chasis). Some graphic cards operate differently however, and the airflow migt be different. I suggest before you buy any fans, take a thin strip of tissue paper, and test the general airflow direction of the casing first.

From what I gather, there's only proper mountings for a front intake fan (a filter is provided, so don't have to worry about dust) and a read exhaust fan. I suggest to stick to these. Only put an intake fan at the side if you can confirm it's an intake vent. Otherwise, you may just mess up the graphic card airflow. If you're willing to do some modding, bottom intake and top exhaust really really help in cooling, but I'm not sure if your casing dimensions will allow that. Note that putting an intake fan at the side might be limited due to the ready made perforations of the side pane. Maybe buy a cheapo no-brand 12 and 9 cm fan to see if the screw holes can align.

Another note, if yo are changing to a third party heat sink/fan for your processor, the fan orientation will affect airflow too.

If I were you, I'd scrap the soundcard and get a better harddrive + a CM690 only extra RM80 for the CM690. (RM220 At www.yeahstore.com) or at least, order the CM590. much better airflow with top blow off vents as well.

Unless you really have high quality 5 channel speakers (or your mobo no onboard sound), I really don't see the point.