We used rosemary sprigs for the skewers (bought fresh rosemary and scraped the leaves off, except for the tips) and I think that added some woodsy heartiness to the seafood. I also added a tiny bit of salt and pepper to the skewers, although the recipe didn't call for any extra seasonings. Not sure it's necessary, especially on the shrimp because the pancetta adds a TON of flavor. If you do choose to add a little seasonings though, be sure not to overdo the salt because the pancetta itself is very salty.
For two of us, we just bought 1/2 lb jumbo shrimp prawns (we got 26-30 ct) and 1/2 lb large sea scallops, which was a good amount for us. We cooked the skewers for about 10 minutes total on medium heat and they were done perfectly! For a side, we just soaked some corn on the cob in water for about 20 minutes (so they don't burn), and threw them on the grill with the husks on, cooking over medium-high heat for about 25 minutes total.
from Williams-Sonoma Essentials of Grilling
18 jumbo shrimp prawns, about 1.25 lb total weight, peeled and deveined with tails intact
3-6 slices pancetta, cut into 18 strips each 3 inches long
18 large sea scallops, about 1.5 lb total weight
18 rosemary skewers soaked for 30 minutes and drained, or other skewers
Prepare a charcoal or gas grill for direct grilling over medium-high heat. Oil the grill rack.
Wrap each shrimp in a strip of pancetta. Carefully thread the wrapped shrimp and scallops on skewers, dividing evenly.
Grill the skewers directly over the heat elements. Cook, turning once, until the pancetta begins to brown and the shrimp and scallops are opaque throughout but still moist at the center when tested with a knife, 3-5 minutes per side.