What areas on the light rail line have low crime and vagrant populations (tent cities, public defecation and drug use etc)?

Pretty much none of them.

Do you have vermin issues, and is it widespread or localized?

Not really. This is a very steep and not swampy part of the world. Vermin is mostly limited to raccoons and rats, and those even really only in the Pioneer Square / downtown / near a restaurant areas. Which you won't be living near because they also have homeless people and crime and tent cities nearby.

Are pets allowed in resturants and grocery stores, or is that looked down upon?

We're among the most pet-friendly parts of the country if not the world.

So a weird grab bag of questions. There's shittons more homeless here than anywhere you've probably lived, unless you're coming here from San Francisco or LA, and if you were you wouldn't have these dumb questions.

The light rail is great, but limited to a few major areas, which are both among the most expensive now as well as most likely to encounter dozens of homeless a day. Tent cities are all over near the highways now too, as well as near major parks at night (with one or two exceptions).

Car-free is doable anywhere there's a bus line and the city grid is the old compact streets laid out prior to 1950s suburban build-out. If you can afford rent, literally any neighborhood south of 85th St in the north, or north of Renton in the South, will let you live reasonably car free.

Like all cities your quality of life can vary wildly depending on how close to crime centers you land. Property crime is endemic, every area has that. But the murders and shootings you should probably check out a map of where those tend to be, and plan accordingly.

One other thing. Just because it looks walkable on a map, might mean entirely different reality because it is steep. We can get 15, 18 degree slopes and rises and falls of 100 feet in 1-3 city blocks around here. That sounds fine on a treadmill stair climber, but it's not as fun if you're attempting to lug home a backpack full of textbooks. Just be aware where the hills are (all over, and they mostly run on ridge lines N/S) and plan accordingly.

Good luck.

I'm baffled by why you called out vagrant populations. If those bother you a lot, don't come to the West Coast. They're everywhere around here. We're the homeless capital of the USA.