On the Oregon Coast your best bet for art, beach, and eating well is probably Cannon Beach on the North Coast, or Newport on the Central Coast. I’m also partial to Astoria (where I live part-time) for everything you listed, except it’s about 10 miles inland from the beaches, on the south bank of the Columbia River (which is about 4 miles wide at that point, so it feels more like a bay). In all the above places there are plenty of hotels, motels, and beds and breakfasts.
You should have no problem finding something in Portland. I would recommend a downtown hotel – downtown is famously walkable. You may find some good deals on the Travel Portland.