Leaving Astoria in early May? Bring lots of down and a snow shovel. The passes should be fine by early June. I rarely carry much extra food and with the Trans Am route, there are plenty of food spots although there are three stretches where you have to be careful. WRT water, just bring a Sawyer Squeeze attached to a 2L Evernew bladder and 2 water bottles. There is water everywhere pretty much. Food? Just stop and buy what is available. I rarely carry a stove anymore when bike touring or backpacking.
Planning day to day? You will throw that out the window within the first week. Motels are not hard to find during the week but more challenging on weekends or during salmon run time.
I think a tour is more fun when you don't plan. Some of my best ones were when I just went from village to village and stopped whenever I wanted.
The ACA electronic maps to load on your Garmin have every single piece of information you could want.