Brassicas get about knee high but are only attractive after a frost which raises the sugar content in the plant. If you have any drought conditions forget about planting. Deer will eat anything so I wouldn't worry about the height of the plants. Buying a couple of auto-feeders spacing them around your property may be more cost effective. Corn will draw deer and give them carbohydrates. If you do plant food plots get a soil ph check, fertilize after you get the soil check so you know what type of fertilizer to buy. With enough rain, clover is by far the best at drawing deer in. With proper care clover should give you about 4 years before you have to re-plant. Over seeding in the spring probably makes sense too.