I've never done this as a loop but it looks like fun. Tons of places to stop on the way. I don't know much about hikes, though. These are a few of my favorite things to do:
Multnomah Falls is a necessity. It's just past the edge of the metro area, so try to hit it right when it opens, as it is very busy and the parking lot gets closed in the afternoon.
Hood River is a pretty cool town. Whenever I go, I always stop at
Pfriem, which just off I-84 in Hood River's new riverfront area. Good lunch spot.
When you head south of Hood River, you get into apple country. If you're coming soon, apples won't be in season, but there are still several places along the road that grow/sell more than that and will be open. There's a spot called the White House that is neat to walk around for a bit.
Once you've come around Mt. Hood, you could head up to Timberline Lodge, a.k.a., the Overlook from the Shining, which is a bit off the main road.
When you finish the loop in your map, you could definitely head to Edgefield in Troutdale. It is a really unique property. Basically, it's an old poor farm that has been converted into a hotel/winery/brewery/concert venue/restaurant/pub/golf course/movie theater/spa/pool hall with about a dozen separate bars strewn about. Great place to wander about get hammered.