No one can answer the "how much work" question. It depends on your goals, genetics, workout intensity, etc. The forearms can generally take alot of work and recover quickly so don't be afraid to work them a few times a week. I use dumbells at home to do wrist curls/extensions and Captains of Crush grippers at work.
The main thing is to add grip/wrist work into your general workout scheme. Don't use straps for deadlifts, shrugs, etc. until your grip is totally wasted. Try hanging from the bar as long as you can on your last rep of pull-ups. Do hammer grip curls when you work your biceps. Be creative.
When you use the grippers don't do endless reps all the time. Get a model you can barely close and work your grip like any other muscle (e.g. 5x5, 10x3).
One of the best things about impressive forearms is that they're usually visible. Roll up your sleeves and everyone knows you have muscle under your shirt.
Oh and don't forget to eat your spinach, Popeye!