Stevia Cultivation and Yield

I am interested in your stevia plug trays. How and when would the plugs be planted here in Maine, USA?

Plant after the last frost date. It is probably around May 15. Space plants 20 centimeters apart and leave 50 centimeters between rows. This spacing will require about 40,000 plants per acre or 100,000 plants per hectare.
Stevia will need good drainage and a steady supply of water. Irrigation is probably a must in most areas.

What could I reasonably expect in yield from the dried leaves per plant?

The plants will probably mature about August. Harvest just as flowers start to form. Since your harvest of dried leaves per hectare should be about 2,000 to 3000 Kilograms each plant therefore yields 20 to 30 grams of dried leaves.
Make sure you remove the stems, because they have such a bitter taste, that not even livestock will eat them.