I have done over 11,000 miles of self-contained, fully-loaded touring in the U.S. and southern Spain. A few things....
1. Anecdotal evidence tends to show that taking a trip like this with strangers usually doesn't work out. I crosed the country with a small (13 people), organized tour. Had it been just me and a few of the group members, I would have parted with them early on. You need to find people who are very compatible in terms of riding capability and other aspects such as willingness to ride in the rain. If you budget based on the assumption that you are going to camp most of the time and share food expenses and your companion is going to leave you for a motel and a restaurant every time it rains or it's buggy, you are going to have to deal with that. Be prepared, both psychologically and practically, to end up by yourself. And by practically, I mean don't plan to share gear like a tent or cooking equipment unless you are will and able to obtain your own if things don't work out.
2. Going south to north along the Pacific coast in summer will likely wear you down to the eraser. Strong winds are usually out of the NW. Also, heading south there are vastly more stretches with shoulders since the overhwelming trend for riders is N-S.
3. Look into Adventure Cycling Association maps. They have several cross country routes and offshoots. The maps show the locations of numerous different services, including campgrounds, grocery stores, motels and bike shops. Takes care of a lot of the planning. Their Northern Tier route runs from Maine to WA, where you can pick up their Pacific Coast route down to SoCal. It passes just to the east of Seattle. You can catch a ferry from Bremmerton into town.
4. Unless you are in really remote places like on American's Lonelest Highway, finding food and water is usually not a problem. Even little towns tend to have at least a cafe and maybe even a small grocery store.
5. Late spring is a good time to go E-W because you don't end up riding through the heat belt at the hight of summer. W-E starting in late spring could pose weather/pass problems depending on your route and how this winter goes.
6. Any donations you collect will not be deductible by the donor unless they are given directly to a charitable organization. If you intend to fund your trip with donations (something I personalyl would never do), make that crystal clear.
7. While you can tour on the cheap, you will likely end up spending more than you plan to unless your budget is unrealistically high to start with. (That happens. In Spain I sepnt about half of what I thought I would.) Budget for things like replacement tires and other bike repairs as well as the "I just don't feel like camping tonight" motel expenditures. I am usually skeptical of the people who claim they eat a bowl of oat meal for breakfast, a PB&J sandwich, a banana and some nuts for lunch and rice and beans for dinner, thereby spending $7/day on food. What are these people doing? Riding 30 flat miles/day? As Neil notes, and as I can attest to, you food intake is going to be high. It's going to be even higher in hilly/mountainous terrain. Even the lighter eaters among our x-country group realized that cereal was thing you ate in the morning to get you to the cafe 15 miles down the road where you had a second breakfast of pancakes or an omelet. Riding day after day after day will likely boost your metabolism a good amount.