im not sure how long you plan on doing this drive in but if you want to do it in one stint here are some reocmmended times to leave.
I'm not sure how long it takes from LA to wherever you are so factor that in but i left LA at 4am coming back here and we just about missed rush hour in every city just heading straight up the I-5. We hit it a bit in Portland but other than that it was smooth sailing and we got here at about midnight. I am right near the US border so downtown Van would be about another half hour.
Then same thing on the way to LA, we left here at 4am (so 330 if from downtown Vancouver) and hit it again a tiny bit in Portland and got to LA at midnight also. Seattle is about 2 hours into the journey so I'd say as long as you beat that traffic you are good.
As far as driving tips...we just planned out what gas stations to go to about 100km's (60 miles) in advance on the navi, since they get pretty rare at some points. Make sure you know how much your car can get to the tank for highway driving and like i said, plan ahead for where to get gas. Also make sure the gas stations you do go to are close to the highway. I tried not to stray too far just in case...never know what weirdos are out there.
Hope that helps.
I can't say anything about the coastal highway but from what i've heard it is only worth it going south as the median will block 90% of the view when heading up this direction.