Since I'm the OP, and I did my trip, let me explain all the details. I borrowed a wheeled case, and I forget which brand it is now but it was a decent one, packed the bike and all the other bike related hardware into the box. I put all my bike clothes in my wheeled suitcase. I was dropped off at Newark, so that was easy, and the checkin took my bag and case (which they only charged me $40 for both). In Seattle, I picked up my stuff and started looking for the light rail. That was problem #1 because it isn't near the terminal but at the very far end of the parking. Nothing like walking past an entire garage to make you think it isn't worth the hassle to take the train.

Walking with the case and the suitcase being dragged behind me was actually difficult. The case weighed 50 pounds altogether. I took the rail to downtown Seattle and got off. Now I was in the streets of Seattle, at about 11am on a weekday, and had a case that wouldn't fit in most taxis. My hotel was up the hill from downtown and I would never be able to walk it with the luggage (even though I walked it many times once I unloaded.) I remembered at one point that the suitcase was convertible to a backpack and I did that, but it was still awkward. I called the hotel and they sent their shuttle van to get me, but I had to meet it at a point about 10 blocks from where I was. I walked that. The case barely fit in the shuttle van because it was set up for maximum # of passengers.

It is possible to do the box and one suitcase, but I'm glad I didn't have any more. If I do it again I'll ship the bike in advance. I doubt I'll get so lucky next time with the checked bag fee too, the guy at the counter was being really nice about not charging the extra fee. On the way back they charged more, but still not the full published amount. And come to think of it, I had another small box to carry on the was back. I think I tied it to the suitcase.