Hello & Welcome Totalnovice !
I am in growing zone 4b, in the State of Michigan. Sometimes low temperatures can go down to -30F (-34C). That's the absolute lowest a mature lavender plant will tolerate.
I have about 60 lavender plants in my perennial beds. Some are 40 years old. The soil must be well draining - never standing water. They love full sun.
I like your idea of a lavender hedge. You would want to plant a row of lavender plants about 24" (60cm) apart. The scent would be heavenly. Under normal conditions it would take three years for the plants to spread and fill in to form your hedge. If a plant should spread beyond your desired layout - just use hedge trimmers to prune. Never trim the wood stems, only the soft needle-like leaves and flower stems. I notice they trim up nicely in the fall.
See in the picture there two lavender plants in this perennial bed, just coming into bloom. Depending on the lavender variety, the height/width can be 12" to 42" (30-106cm) when in full bloom.
I wish you the best of luck with your garden.