There's some pretty good advice here.
Even so -- here's some basics I've learned over the last couple years.
Fan specs and ratings: Voltage, amperage, CFM (min and max if the speed is variable), size (80mm, 92mm, 120mm -- also by width: 15mm, 25mm, 38mm), RPM, and noise (dBA). Generally, except for minor differences in fan design, fans of the same size will push the same order of magnitude in CFM at the same RPM, and maximum RPM is a linear function of the amperage rating.
All our computers provide 12V(olts) for fans. Fan "tails" -- the power and sensor plugs -- can be modded to make the fan run on 7VDC or 5VDC -- which means that the fans will run slower, quieter, and with less air-flow (CFM).
Noise ratings are not the final arbiter of a fan's "acceptability" if you plan to run the fan at a lower speed -- by either changing the tail, controlling speed through the motherboard, or through a front-panel fan-controller. There are two types of noise: motor or bearing noise, and "white-noise" from air-turbulence. The bearing/motor noise is the most irritating, and fans of lower quality can produce more of it at their top-end speed.
Noise can be muffled by choice of fan placement, grommets or "shock-absorbers" that isolate the fan-frame from the computer chassis, various "ducting mods" to the motherboard, and noise-deadening rubber pads applied to the inside of the case panels.
Positive air-pressure inside the case is a good thing. Creating a vacuum inside the case is a bad thing. You want to at least balance the CFM of intake fans with that of the exhaust fans, or otherwise make intake CFM slightly greater than the exhaust CFM. By this I mean that the fan-spec CFM should be added up on the intake side and the exhaust side -- ultimately, the "true" exhaust CFM should approximately equal the intake CFM even if the "potential" CFM at the exhaust side is lower than the intake. Interior air-pressure and exterior air-pressure will equalize and more air will exhaust through the exhaust fans even if the fans are only capable of something less than what the intake fans are pushing through.
So it isn't necessarily the number of fans -- but their cumulative CFMs -- which should be chosen carefully on the intake and exhaust side.
And as the other members have said, larger fans push more air with less noise.
Many motherboards are capable of providing current or amperage of at least 2 Amps, and most of the fans you find on the market for cases or CPU cooling are rated at between 0.2 A and 0.8A. If the motherboard manual says the limit is 0.78A per motherboard fan-plug OR a total of 2.34 A, you should be able to use a single plug to power one or more fans up to that limit -- assuming you don't use the other plugs for anything other than fan-speed monitoring. Personally, I try to keep cumulative power to fans connected to the motherboard under about half of the total spec. But attaching more than one fan in parallel to a single plug should be approached cautiously. The easiest thing to do is to use more than one fan of the same model (and amperage) -- and use the yellow monitoring wire of a single fan for that purpose.
My personal view is that you are better off choosing a fan with a higher amperage and rpm ( or something more than "needed") and then running the fan at whatever speed you choose to mitigate noise and provide the required CFM. A "beefier" fan-motor may be quieter at lower speeds, and running such fans at lower speeds should extend their life.
Oh yeah. Another thing. Fan specs include information on the type of bearing used and the MTBF or mean time between/before failures. Sleeve bearings are less desirable for CPU cooling -- ball bearings are more desirable. Pick a fan with a 50,000-hour MTBF or higher for CPU cooling.
Given the price of the case you've chosen, I wouldn't hesitate to modify it with a Dremel or nibbler tool to accommodate larger fans, but that's a matter for you to decide.
I will add something about the psu fan swap. Although you are a "1st timer" & while it CAN be dangerous, the fan swap can be super easy. Mainly depends on the brand psu you go with. PM me if ever you feel liking taking this on. I'll be glad to help.
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