You don't really have to cut them back, but once the leaves get to be full sized you might as well cut and use them as they just end up shading the other new leaves if you don't, and start to degrade. When it bolts the new leaves will also be a different shape and in my opinion, a little bit bitter tasting.
I would recommend bringing them inside if possible considering your growing zone. While they will grow for 2 or 3 months in mild weather, once it gets above about 75F for a few days in a row after they are mature, then they will start to bolt.
For this reason I always do an early spring and late fall crop. I have it growing in pots so once the plant has produced seed and starts drying out, I bring the pots inside for a couple months so they stay dry and out of wind. After the two months (maybe 3 to 4 months for you) I harvest the seed, inevitably knocking a few off onto the soil that I leave behind. I sprinkle 1/4" of soil over them and start them again outside.
I do dehydrate it a lot, just placed on racks with mild fan forced air. It does lose a fair amount of taste but some remains, almost like it is a different but still related spice. I suppose you could say the same about a lot of different spices when comparing fresh vs dried.