I assume shrimping is done in Washington the same as here in AK. I generally look for 300' but bottom structure is more important than depth. You want the steepest, roughest country you can find but be careful you don't let the pot drift into deeper water where it will either sink the buoy or float off if your buoy is big enough to float the pot.
Bait choice doesn't seem critical. Everyone you talk to uses a bait that they swear is the best and range from cat food to a salmon carcass, and they all catch shrimp. I set all 5 pots individually because I pull with an anchor buoy system. If you have a pot puller you can put all the pots in one string, but you will loose the ability to prospect different areas. Some folks say they can see schools of spots on their sonar but I've never seen it.
Sometimes it seems to be hit or miss. I've got areas that usually produce shrimp but occasionally an area will seem to be devoid of shrimp that normally produces well. Last year I had 2 pots on a shelf at the same depth about 50 yds apart. One pot had 118 shrimp (the most I've ever had in a pot) and the other had 9, so who knows exactly what's going on down there.
Something else I've found is that using an expensive, pretty, round orange buoy seems to increase the chances that it won't be there when you come back. I think that when people assume their pot has been stolen what often happened is that someone cut the line and stole the buoy. I now use old liquid laundry soap bottles filled with foam as buoys and haven't lost one yet!!