I usually pinch the end of branches to get it as bushy as possible when it is small. And then I start harvesting once it gets about 10 inches tall. I usually start mine in the fall inside the house and then come spring
when it is time to put them outside they are good sized plants. As far as harvesting. I harvest the larger leaves equally from all over the plant. I probably never take more than 10 to 20 percent of the plant at any one time.