I lived in Portland for a long time and still get up into the Northwest a few times a year. It's a beautiful part of the world, very topographically diverse, and with some pretty interesting cultural facets, though nothing as cosmopolitan as the big international cities (except Vancouver, BC, I suppose).
You don't want to rely on public transport except within the cities; some of them have good bus systems, but bus or train transport even between cities is inconvenient, and to anything except the cities and larger towns of the Interstate 5 corridor, it's nonexistent.
The US doesn't really have the concept of tourist "excursion" busses to points of interest. In most countries you can fly in and ask the hotel desk "How do I get to XYZ National Park?" and they send you to the right train station or bus station---in the States they'll say "Well, you drive across the Ross Island Bridge and get on Interstate 5 south, and then in about an hour you exit at..."
I don't think you'll have any difficulty driving there, though; road signs tend to be good, speed limits are posted, and so on, and in that part of the country the normal driving is quite non-aggressive, especially by international standards.
Food in the cities will not be a problem. Portland, Seattle, and Vancouver have every cuisine imaginable, and there's a big cultural movement there for vegetarian foods, locally raised food, "exotic" (to Americans) cuisines. Simple vegetarian food is easy---this is an area where you can *expect* that if you walk into a restaurant and say "I'm a gluten-intolerant vegan", they will immediately be able to tell you what they have that you can eat. (There are halal restaurants and groceries, also, if that's your concern about "forbidden meat".) You might want to spend most of your stay based in Seattle or Portland, with one- or two-day trips out into the field where you can take food along---but there's certainly no need to plan for a diet consisting solely of Tasty Bites!
Places to photograph: depends on what you want to photograph! The Columbia River Gorge and the Cascade and Coast mountain ranges are the obvious places for landscapes, and that stretch of coast is probably the most beautiful rocky coastline anywhere in the world. The cities would be OK for street photography, I suppose, but not in the "endless crowds" way of a big international city---you might do best to find places where an Event is going on. What are you looking for?