Rookie

To get miles per hour from knots; multiply knots by 1.151 For most of our purposes, consider them the same. Trolling speed will depend on a number of things like the type of salmon you are fishing for (faster for coho and blackmouth, a bit slower for kings), the type of gear you are trolling and the tides or currents.
As far as jigging in 400' for salmon, I don't know anyone who does, though some commercial trollers get down pretty deep. Most of the salmon fishing that I'm aware of takes place in the top 200' of water. It is very tough to fish deeper due to the weights involved and currents. For jigging, concentrate on 90 - 140' where a bank drops off. Fish near the bottom unless you see schools of bait fish suspended. Mid Channel Bank, Jeff Head and the edges of Possession Bar would be good places to try jigging for blackmouth. I haven't checked the regs yet, but I think they are all open on Feb 16. I would recommend that you either take a salmon fishing course or join a club like Puget Sound Anglers or other similar club. It will cut your learning curve way back.

Good luck
Scott