We find the traffic from the contruction worse coming away from children's, not going towards it. Assuming you are coming the 520/montlake way. You may want to take 25th to 65th back to I-5 on the way home.
It rains a fair amount but not constantly and not too much in the summer. From your description it sounds like you'd be happy in Portland, Seattle, or Vancouver BC. I like almost everything BUT the weather here, so you'd likely be pretty happy . If you have less patience with people who are "slow to warm" you might not love Seattle or Oly, but people are great when you get to know them.
I've had success beyond what I had hoped with the rodgers alarm from the bedwetting store online (you can get the malem alarm there too). We've followed the instructions they gave us, including not restricting fluids or waking to take to the bathroom, and been very successful. He has had lots of dry nights and almost never had any previously (we've been using it about 3 weeks), and if he wets he only wets a tiny bit and then the alarm gets him up - he is VERY difficult...
If you found a place in NE Seattle In the Eckstein middle school service area you could choose between a K-8 (Jane Addams) an alt (AS1) and Eckstein. You can find the service area maps on seattle school district website.
I would personally visit some of the private schools and ask them how they would support and accommodate your son. We only have experience with british private school at the nursery level, but we met many parents with older kids that were there because of bullying and boredom type issues, and I was very impressed with the school in general.
I also think the boarding school seems like a reasonable option, I just wouldn't want to leave any stone unturned. Best of luck...
I appreciate this thread, there seem to be more people in our situation than I realized. We also had not so much luck with the traffic light system in 1st grade... the teacher stopped using it with him, but things didn't improve much and he was miserable and unchallenged on top of his sensory difficulties, so we are homeschooling and doing OT for the rest of this year.