Antirem, go to SacredCactus.com. This is the best place for growing instructions. Yes, I was just kidding about the music and yes, all cacti taste pretty much the same...horrible.
A node is just a spot where the spines are comiing out. When you harvest the cactus, leave a stump tall enough that there at least two of these spots above the dirt. These spots are where new growths will pop out of. I also save the top 4 inches and plant that. They multiply faster than rabbits this way. Just leave the tip to form a dry scab on the bottom ( about a month to be safe ) and set it on top of a pot of dirt and in another month or two you will have root buds. Then you can plant it deeper in the ground. You can only do this in the summer, they stop growing all together in the winter.
One dose a year is about right ( I recomend starting w/ a pound of cactus ). Mine grow about 16 inches between May and September. But you may find that if you leave a stump, it will grow 2,3,or 4 more cacti. Then in a couple years you cut those and more grow. My biggest cactus has 12 tips growing from one stump.