Probably by now you have plants with enough leaves to harvest without hurting the plant. One way is to strip off leaves individually from 1/3 of the plant, another is to simply cut back the plant by 1/3. What remains will continue to grow and produce more leaves, especially if you add a little fertilizer after pruning.
Basil is one herb that doesn’t keep its flavor well when dried. Freezing is probably the best choice. I like to lay the plant material to be frozen on some plastic wrap in a shallow layer, cover with another layer of plastic wrap or roll up. Mash the packet flat, place in plastic freezer bag, squeezing out all the air, and freeze.
So your recipe calls for a cup of loosely packed basil leaves and here you are with this frozen mass. What to do? Before you freeze the basil loosely pack a measuring cup with leaves and weigh on your kitchen scale. When I did this I got .3 ounces. I taped a note saying just that to the inside of a cupboard door. The next time I need that loosely packed cup of basil leaves I can just open the cupboard to see how much that would weigh and get out my handy kitchen scale and the frozen basil. Problem solved. – Sandy