They'll figure it one at some point between being born and becoming fully mature, usually because they start getting weird cravings or more subtle changes. Then, one day, they'll fully transform. It can really be as dramatic or as simple as you want - there is a lot of variety in how these things manifest.

Yeah! Handling your new instincts and thought processes can be difficult, so the first few changes can be a wild ride.

Some kinds of weres may find themselves wanting to hunt, but none of then HAVE to as long as they eat while human. Portland is apparently surrounded by a lot of wooded areas, so that would be your best bet for running freely, though you still have to be careful.