I know nothing about March there, but we went in mid-September 2014 and loved it. Lots of great cycling, and the public transportation is the bomb. Our blog posts might help you plan some of your adventures:
Day 1 -- Urban riding in Portland and visiting the famous Voodoo Donuts:
http://travelingtwosome.weebly.com/t...t-of-doughnuts
Day 2 -- Rural riding on the Vernonia-Banks Trail followed by some unique eats in town
http://travelingtwosome.weebly.com/t...r-with-friends
Day 3 -- Taking the MAX downtown and exploring on foot -- plus more good eats and donuts!
http://travelingtwosome.weebly.com/t...hy-vegan-lunch
I'm sure the TEers who actually live there can help even more, but these posts may help you get a tourist's perspective.