As for the growth rate of redfin pickerel, they don't get big, rarely hits 12" mark, 7-8" is average size for both redfin and grass pickerel.
Yes they can reach up to 12" but that is NOT average size for grass/redfin pickerel. A 12" plus redfin/grass pickerel is a monster or trophy sized.I've had both grass and redfin pickerels. All have reached 12", or just over. I wish I could tell you how long it took to get there, but all I can say is that it didn't seem very long. (My current Redfin has been full size for years now.) I have him in a 215g with a large bluegill.
Remember that you're limited to other fish that are large enough not to be dinner for the largest pickerel in the tank.