That's a nice charge controller that will do most of what you want. If you want to grow your system (plan ahead), you may outgrow the 30A rating.
amps * volts = watts
watts / volts = amps
watts / amps = volts
The key is what kind of amps and volts are your panels putting out? It should say on the back, and it'll pretty much never be exactly 12V.
Let's say it was exactly 12V and 100watts
(100W/12V = 8.33A) So you'll get 16.66 amps out of 2 identical panels, 24.99 out of 3 panels and 33.32 out of 4 panels.
So your 30A controller can handle the 3 panels at full power on a good day. I wouldn't go with 4 panels and round down as it's best to expect peaks and surges.
Take a look at the various panels and you'll see lots of different numbers that add up to the rated watts.
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