Gardening in Pacific NW (specifically, Tacoma WA area)

I am new to the Pacific NW - when is a good time to start my seeds? I have a limited garden space because we live on an army base, however I do have enough to do something. I plan to grow tomatoes, melon, spinach, cucs, and??? Should I start the seeds inside and then transplant to the soil? The soil is VERY rocky; I've never had to deal with that. Should I just turn it real good and leave in the rocks? What about planting the same thing every few weeks to space out the 'harvest' time? Any tips or suggestions?
Thanks!