A. Maybe not enough close together to play a different field every day. You will need time to travel between locations. Maybe eat and sleep too. There are events and different things/shops to investigate across the whole state. Given the fact that you're coming from Canada to a country with actual gun rights, and no sales tax expects some culture shock.
B. It's always polite to ask the store, field, etc., BEFORE you plan to set up and sell stuff out front of their establishments. It's just common courtesy.
C. Yes, there are enough KOAs, campgrounds, BLM, National Forests, and so forth that it's really not that hard to "van camp" and still be close enough to any bathrooms, showers, food, gas, whatever you need. I just depend on if you know where to look. I've given you a link to some the generalized regulations you'll need to be aware of while traveling. It's a good idea to observe these rules no matter where in the state you are. Our officials are pretty chill about it, if you just talk with them and are polite they'll return the favor.
http://www.oregon.gov/ODF/Recreation/pages/Camp.aspxAlso if you plan to do any fishing here are our rules for that.
http://www.eregulations.com/oregon/fishing/As a trip, you'd be a non-resident, but if you sleep you stay in an actual residence, even for a night, you are technically a resident of that location and therefore a resident of the state. So clearly hotels, B&Bs, campgrounds etc, are not actual residences. Just saying. Good luck!!