Cory,
I was there the 20th-24th this year and it was at peak.. 2017 was 24th -28th ..2016-was early 10th -14th every year will be a little different as we never know what mother nature will bring the past few years I have waited to book tickets until I know when peak will be it costs a little more to do it that way but it is a long ways to go to get there and walk around and look at foliage
that has happened before to us.
If I was going to pick a time now to plan ahead would go 22nd -28th it has normally been a good time for bloom there. l will cover all the gardens in my winter thread soon they were awesome this year
and lots to see in Salem. Its been years since I drove the Oregon coast so can't help with suggestions there but enjoyed the views and little restaurants up and down the coast.