A two bottom 12" plow will be fine. Cutting through grass/sod, then inverting the sod so the roots are up to dry and die are what a moldboard plow is supposed to do. You will plow in HST/MED at close to max throttle.
You need to cut grass as short as possible before plowing. Ideally, your plow with have coulters (pronounced colters) which are serrated wheels which slice the verdure before the moldboard plow begins to invert the dirt. (Google: plow coulters, then select IMAGES.)
I retired after 37 years in the wine business, my last 25 years doing sales, marketing and winery administration for California wineries. In California, where conditions are certainly different from Newfoundland, the ground is usually ripped deep with a crawler and claw as the first step in planting vines. The purpose is to fracture deep so the vines can go down 10' or more for increasingly scarce water. Even so, drip irrigation is required for a profitable crop in most years. In California wine grape yields are usually 6-7 tons per acre, if well farmed.
HST transmission is fine for plowing. HST is what I have. Max torque as the plow first enters the ground, just what you need.
Describe your top soil, soil thickness and sub-soil.