Unless you do some serious hiking, back country hiking, wilderness hiking, you won't see much of the Park. It is 99% high country. the west side is rain forest, the HO river area is some great fishing but it is on the reservation, the only road on the westside is 101 and the local town roads.
The east side along hood cannel is tourist haven, and packed all summer.
Just thought you should know.
Our normal suggestion is, up the west side (97) north, stop and see what interests you, across the north cascades highway, (20) west, and down the west side avoiding I-5 at all costs. :)