I lived on the South Hill in Spokane for a couple of years (2 years ago now). I’d usually ride south and hardly ever had issues with cars or people. The roads are nice in WA and many have shoulders. I’d mostly try to keep to smaller roads off the beaten path. Once you get out there you can find gravel roads so there are many possibilities for mixed surface riding.
I liked riding out through Riverside Park all the way to the dam. Camp Sekani was fun for mountain biking or going around there on my gravel bike. The Fish trail is quiet and can be combined with other rides. Getting through/past the center of Spokane on a bike can be tough. I found it hard to ride from the South Hill towards downtown and then get back on a safe road without too many cars though I did finally find some obscure routes.
The 2nd year we were there, there were tons of forest fires and I lost a month of the precious summer riding.
Around October I just put away my road bike because I didn’t want to slip and fall on leaves and I just road my gravel bike everywhere until it got too cold.
You really have to embrace the winter in Spokane so that you don’t go crazy. During snow storms I’d strap on XC skis and go do a workout in Manito Park. My 2nd winter there I joined the YMCA and that helped get me through the winter. We also started doing a kids XC ski program at Mt. Spokane so every Saturday for a few months we were on skis. I once saw a couple of guys going around Riverside park on fat bikes during the winter. If I had stayed longer I would have bought one just to have another winter option.
The only reason I wouldn’t willingly move back given a choice is the daily winter life. Raking leaves in the fall and shoveling snow all winter sucks IMO. 
Don’t buy a house with a giant maple tree if you don’t want to rake up 50 bags of leaves! Taking my kid to school and almost slipping and falling on the icy sidewalk every day for months really sucked! I didn’t know what Yaktrax were. But if you are already used to winter life then ok.