Depends how many your case will allow, and, at what size.
You can probably find this little detail on the specifications section of the manufacture than made it.
As for connecting them to the board. There's multiple ways to go about doing it.
Most mobos have about 5 fan headers on the board (You can also find this detail on the manufacturers page), however, you can use anything from splitters to just running them straight out of the power supply.
With Splitters, you can probably support about 2 fans on one port. I wouldn't recommend any more than that. If they're PWM, keep in mind that the port will treat both as one - Any fan control will affect both of them.
You can use a Fan Controller, in which the fans would be plugged directly in to. How many these support vary greatly depending on which one you buy.
Finally, you can plug them directly into the power supply by means of a Molex cable and adapter. This is the method I use for 6 of my 8 fans, just makes the cable tidying easier when you can hide them behind the tray.
The downside to this is that they will run at full speed constantly, unless you use an additional 5/7v adapter, in which case they will run at that.
For this you will need a Molex tree from your power supply and some Molex-3pin adapter cables. I recommend the braided ones from Bitfenix, but they are a bit pricey.
Oh I almost forgot. With whatever option you pick, you must always have one plugged in to the motherboards CPU_FAN1 header, it tells the board in POST that there's a cooler attached. It won't boot otherwise.