I am no expert by any stretch , but from what I have observed and learned from the MS members is the shallower the water the longer the rods. A lot of people including myself use 12' rods, I have 2-10' 6-12' and 1-14 ' . The more you get into this the more options you'll come up with. Pulling cranks (my favorite) pushing cranks, long lining , spider rigging.
water clarity also adds to the length of the rods The idea is the clearer the the water the further out you want your bait. I highly recommend you go to the MS page and read the pulling cranks article, Use the google search on the site to find the answers to just about every question you could think of about crappie fishing. Personal preference will also way in , I like 12' rods, I just got 4 BnM pro staff trolling rods, these rods can be used for spider rigging the lightest jig/minnow or used to push crank baits with 4 oz weight, very tuff yet sensitive rod. All the MS members I have met or talked with are great people and will help you anyway they can. The crappie camps are a great way to make new friends and learn new tricks .