Fava beans are cool weather crops, which means that they can be planted in late fall or early spring. In San Francisco, where I live, they can be planted almost all year round.
Favas are the perfect crop to rotate between heavy feeders, like tomatoes. In fact, they are the perfect winter cover crop.
Favas can grow to be 2 to 4 feet tall! They don't need a ton of attention, though some people stake them to give them support (mostly so they don't fall over in windy weather).
To get the most nitrogen benefit, cut down the stalks when they flower. If the stalks produce pods, they are taking more nitrogen then are putting in (thus, negating the "nitrogen fixing" properties).