CDA,
If your going to use asphalt shingles; and you live in an area that has hail at least every 3 to 5 years; I'd use a less expensive shingle. Your going to have to replace it before the warranty expires. I also prefer "turtles" over ridge vents; especially if you have several areas that won't be properly served by the ridge vent.
Story: I bought a house that had a large electric controled attic vent; and after a hail storm; told the roofer to replace it with several turtles, when he reroofed it. The hole left from the removal of the electric controled vent was too large to put a turtle in it's place; so, he covered the hole with a sheet of sheet metal and shingled over it. Fortunately I caught it before paying him; made him hire a real carpenter to rip it up and frame the opening properly. If a home inspector or insurance adjuster walked on that space and fell through; it could have cost me plenty.
You have to really watch these roofers; and, he was a local; member of the BB, Chamber of C, and every other orgainzation in town; and, been there for 30 years.
Good Luck,
Uncle Bob