I always pre-cook shrimp, prawns, crabmeat, mussels, salmon, whatever, before adding to pizza, if I don't use the canned stuff. In fact, if I put sausage on a pizza, I precook and drain that too. It makes thinks less sloppy and really doesn't detract much from flavor.
BTW: There only ever two spices I use on Pizzas, Red Cayenne Pepper flakes and Oregano flakes.
Pizza Crusts are another matter and while pizza dough is a simple standard, you can get creative. When I lived in Connecticut, you could buy pizza dough balls in the stores. Here in California, that's not so.