There's a quick globe image in the pilot that pegs Metropolis as somewhere around Delaware, if memory serves. I believe it's when Clark is flying to China to pick up the dinner he and Lois share while working late. But the show was also very inconsistent. Metropolis clearly has a harbor, but when Nor and company come, Metropolis is shown as land-locked, for instance. In the recent Justice League/Batman vs Superman movies, Metropolis and Gotham are shown as being relatively close to one another. You can basically get away with as much as you'd like in your writing.
As for the elections, yes, the two party system covers it all, from federal down to the local positions. At the most local level (for towns and cities) you'd also have Mayors. Once in a while you might get an outlier that runs (ie. Tom Jones of the Green Party or Jessica Smith of the Libertarians). But any "third party" basically has a snowball's chance in a furnace of getting elected. I don't think I've ever seen it happen where I've lived. Each state has certain powers independent of the federal government. For example and to use something current, New York might implement a mask mandate while Florida might opt not to make it mandatory to work, shop, or go to school. Each state has its own sales tax, etc. (It might be 6% in Connecticut and 8% in New York.)
I'll leave any questions on the criminal system to those who are more knowledgeable than I am.
