The bike/multi-use trails in town are a love/hate relationship. So many good stretches, but mixed with streets it just becames a PITA. I feel like the western part of town is a maze knowing where there are trails (if you haven't investigated it in advance). Not to mention, I always feel safer crossing intersections in the street rather than on the path. Roads in this section are also busier and I'm not going to lie, taking the lane on 42nd makes me a bit nervous.
With regards to road rides, I think you can put in some decent beginner rides on the greenway assuming you are willing to deal with sporadic ped traffic. Entire loop + EGF side is 20 miles or so? Which begins my next rant: the intersection at the point bridge. Talk about getting out of a ride groove to go through that light. They should extend the trail below the point bridge, then build a ped/bike bridge across the river so the greenway feels less disjointed.
My typical GF loop = See below
http://www.mapmyride.com/routes/view/63857878Greenway loop: is anywhere from 10-20 miles