Yes, it should work with those motors.
But, if you can come up with another $40, I'd buy these instead.
3.6V,3A,1.8 Deg. NEMA 23 Step Motor-MPJA, Inc.
Just watch out for shipping.
The capacitor included with the kit is to make an unregulated power supply. If you use a switching supply like the one on Ebay, you don't need the capacitor.
The power supply requirements will be dictated by the motors you choose, and possibly your wallet.
What do you plan on using these for? If your building a CNC, then you really don't need to buy the electronics until your ready to install them. Then you'll have a better idea of what you need. Buying motors and electronics first is a mistake that's made wuite often by new builders.