Are you going to ride in Seattle, Bellevue, or both? Where do you plan to stay?

The answers to everything you just asked vary a lot depending where you are. I've heard helmet laws are enforced in the financial district in downtown Seattle. I haven't seen or heard of people having an issue otherwise. Some of the bike lanes and MUPs are very useful. I wouldn't take the lane on Aurora unless I was feeling suicidal but most streets aren't a problem. I can't say much about where to ride or avoid east of the lake.