If you use H-Bridge ICs, they may already have flyback diodes installed. If they do not, they are a smart thing to add. Other than that, the IC really doesn't typically need anything extra. For my TA7291S chips for example, you have IN1 and IN2 which control forward or reverse, and you have OUT1 and OUT2 which you wire up to your motors. These also have the flyback diodes built in. Look at the datasheet for a "typical application circuit." I attached it.The S comes in a really compact SIP package which I find nice to work with. You would need one for each motor. The L298 ICs are quite different, but they do have two H-bridges in them, so you can control 2 motors with one IC.However, since these cannot handle 6A directly, point me to some of the ones you found and I might be able to give you a hand with putting the circuit together.
It looks like you would only need a few common components to get that H-Bridge running. The examples show a PWM chip being used, but if you will be using the PWM from the arudion, you don't need that. The bootstrap caps are necessary. Depending on whether you wish to use the current sense output, it looks like you may need a few more common components.I have learned one thing from looking around at these.... I am in the wrong business. Good Lord on these prices. Ridiculous!
Guessing - I haven't used one, but I'd assume that the current sensing pin gives you the opportunity to measure the current the motor is pulling, on the arduino by using analogread and doing a little math. This would let you detect when your motors are stalled.