Magness Memorial Tree Farm is in Sherwood 6 miles way and they have hiking trails. The Areospace museum is right there in Newberg. It contains the original Spruce Goose. There is a waterslide right next door as well. I am sure there are many bike trails as there are all over Oregon. Maybe check at a bike shop for maps.
The Allison Inn and Spa is about 45- 50 minutes from the Portland Airport. I think if you plan to visit the Williamette Valley region for more then 2 days you should stay at the Allison Inn and Spa or some other place in the Newberg area. Traffic in and out of Portland can be heavy and it will add time onto your day. Depending on how much time you have I would spend 1-2 nights in Portland. There are attractions there worth seeing and the restaurants are very good.
I hope this helps you.