A hotel in the downtown area should work. Public transp is v. good here - buses + light rail (the MAX or the streetcar) - see trimet.org, so you def can get by w/o a car. I like the Riverside Marriott because my employer uses it. It is close to the streetcar & the waterfront park.
What to visit ? Where to start... Japanese Garden, Chinese Garden, Rose Garden / Washington park, Pioneer courthouse square, the waterfront park I mentioned above, ... there's more but i can't think of it all.
For food, check out the world-famous food carts - http://www.foodcartsportland.com/maps/
, the bigger the pod the larger the selection. Voodoo doughnuts if you like fatty dough. Def a brewery. The more sophist. restaurants like Andina or Le Pigeon are also recommended.
Try review sites like tripadvisor, yelp, etc for more ideas.