A good route! One small correction - you will skirt the Dartmoor National Park rather that Exmoor.
Did this route before my ride back to Sussex. Some very good twistys and straights, nice road from Torbay to totnes to start with, nice gentle bends and views of south hams. Through totnes and onwards on A38 towards Plymouth. Turn off onto A386 signed to Tavistock, all the way skirting the exmoor national park, fantastic views, real sense of space, some good twists and flat outs. Watch out for numerous dead bunnys in road, pheasants etc, then bit of A39 to Bridgewater, turn off onto the A377 to Exeter. A road to round off the tyres, road has been notorious for bad surface, lots of ridges and loose gravel etc, but road this March 2012 and is much improved. There are now road markings in the foresty bit which is a plus.!! Watch out for the odd large rock and natures creatures to keep you on your toes. Still parts of the road are scumbly and ridges in places but on a good spring day, no probs. Then before you enter Exeter, the A380 blast back into the English Riviera. Cheers!!!