But in an at-large election, with four seats in play, does the voter pick one or four candidates?
That's a good question. I assumed each voter picks only ONE candidate. If each voter picks up to four candidates, then your concern about the big cities dominating a statewide race would be a valid one.
There's also an intriguing option where each voter is given four ballots and can pick up to four candidates, but can also opt to cast multiple votes for a candidate. Basically, a voter can vote for four different candidates, cast four votes for one candidate, or anything in between. I'm not sure that's a good idea, but it would definitely make things interesting and unpredictable.