To find the actual grade log into the "Ride with GPS" website, you'll have to sign up but it's free. Use it to map your route through the area you're concerned about. I live in the area and no it is not that steep but it does have some pretty good hills heading south from Hwy20. The road has shoulders off and on and there is a lot of traffic from commuters and tourists. The bridge is used by cyclists and is legal but as mentioned by another posting it is barely wide enough for two trucks to go past each other which is why I have always avoided riding it, however since I'm planning to ride the PCH boarder to boarder I will have to. Maybe if you can time it early or late in the day.
As far as camping, yes, you will get bombarded by jets in that area, I gave up hiking the trails around there because of it. A better campground on the mainland is Bayview State Park next to Padilla Bay not sure of the mileage between the two, maybe 15-20 with only about 2 of them on Hwy20 which does have a good wide shoulder. Don't know if this helps with not knowing just what kind of tour you're doing.
If I can be of any more help, email@example.com
I ride this area all the time so I know the roads well.
Good luck & ride safe