Tom;
No such thing as a dumb question.
I wash the planks and for short fish cooks, you can use them three or even four times. They'll then fall apart and you can use the scraps for smoke wood.
However, when doing long cooks (like my "famous" meatloaf on a plank) one or two cooks is all. In fact, I ALWAYS (now) start long cooks with new planks.
I dump one lit chimney of charcoal, spread evenly over the charcoal grate for "medium" heat. I pre-heat the food side of the plank for TWO minutes to sterilize it. Then, I flip it and add the food when the plank starts smoking. That way, you have smoke even for short ten to fifteen minutes. Using a Weber OTG or Performer, you can cut the bottom vent down to control the heat. Too hot and you can set the plank on fire, too little and you don't have any smoke. Just mild smoke is all you need or want.
Keep on smokin',
Dale53