I am from the metro Detroit area originally so this metro area seems small to me (both cities, they run together). I am pretty sure that around half of the state's population (around 5 mill) live in the metro area. A metro area of 2.5 mill isn't really very big.
Sales tax - I don't know what exactly the state charges sales tax - on I think we have paid sales tax on a computer and that's about it. No tax on food and clothing. I don't know anything about how taxes would work on his wages. Are you saying that he needs to pay state income tax out of that? As far as I know, prevailing wage is usually quite generous. I think the state taxes here are a little higher due to some of the wonderful programs here like MinnesotaCare, our state's subsidized healthcare program, but nothing unreasonable.
I didn't really find that rent was any cheaper in the burbs than in the city - it is more of what neighborhood you pick. Actually I think many of burbs are more expensive than the city. Craigslist has the run on rentals ads here, but there are still lots of people who just put signs in their yards. Minneapolis and Saint Paul are both very safe cities - the only area I wouldn't live is North Minneapolis but I know people who live there and think it's fine. We live in St Paul's Westside neighborhood. I also like the Como area in St Paul and NE Minneapolis for areas in the city. Lots of API families in S. Minneapolis.
Weather depends - it was pretty cold last summer until September when all the parks and beaches closed up for the year! Generally, July is nice to be outside, possibly some hail/tornadoes/straight line winds. People here think it gets hot (maybe you will too since you're from OR) but I don't think it does. There are definitely 4 seasons here and I greatly enjoy fall. Once November rolls around, winter is pretty much here and you can count on snow on the ground from Nov - March. Not because it snows a lot but because it never melts. We have had a very mild winter this year with only a short stretch of subzero temps!
There are tons of things to do here. People really live up the summer here and there are festivals just because...The API group is active and has playdates all week, there are tons of museums, parks, libraries, rec centers, and nature centers. We like to go to the "little zoo" in Como Park in St Paul which is free, the "big zoo" in Apple Valley, the Children's Museum in St Paul, the sculpture garden in Minneapolis, Harriet Island Park, farmer's markets, really I could go on and on. I have been to dozens of places in the last 2 years since we moved here and haven't scratched the surface. There are several indoor playgrounds for the kids to play on in the winter. Lots to do.