I strongly suggest using the Seven Devils Road from Charleston to Bandon. On my second trip I decided to bypass that route and take 101. Big mistake. There were sections south of Coos Bay where the shoulder was nonexistent, and when a shoulder existed, it was narrow. That was a stressful stretch. Yes, there is a steep climb out of Charleston on the ACA route, but it is not that steep and not than long and once on top there are no significant climbs. Plus, the climb is worth it for the solitude and lack of traffic. A much more pleasant way to reach Bandon.
The Astoria Bridge was challenging but I found the drivers were accommodating.
I have elected to walk my bike across a few of he bridges in Oregon using the sidewalk, particularly the bridge north of Coos Bay. I liked the calmness of walking and stopping on the walkway to see what I was crossing.
In Oregon you have two tunnels. Be sure to use the warning lights at the beginning of the tunnels then pedal hard.
Whenever possible take the alternative route that will keep you off 101, particularly in California. As an example, in Oregon the route from Neskowin to Otis through the Siuslaw National Forest over the back shoulder of Cascade Head is a joy. Traffic is nearly nonexistent and the forest seems primeval. Also, the Three Capes Scenic Route from Tillamook is a much better option than staying on 101. More climbing but much more scenic and far less traffic.
Your May/June date will find the weather still iffy and likely extensive fog on CA 1 in Northern California. If you have not already done so, I suggest a flashing rear light for safety. And as already discussed, I have found a side mirror very helpful.
As others have said, this is a wonderful bike route. Oregon is very bicycle friendly. Great roadside parks (the park on the southside of Florence is incredibly nice). California is less bicycle friendly in that the roads have less of a shoulder and, in the case of CA 1, zero shoulder. The Washington part of the ride is okay and the shoulders are better than California.
Enjoy the journey.