I don't know if I'd say good, but I think Hans would've been an adequate ruler. If he planned to hurt the people of Arendelle, I think he would've done it after Anna left him in charge. He didn't think she oder Elsa would be back, and the people would've been too frightened of the eternal winter to challenge him. He had the opportunity, but he didn't take it. Instead he treated them with respect and made sure they were fed and warm, so he couldn't make too bad a king.
Also, Hans only tries to harm people when they stand in the way of something he wants, so I think his reign would work like a trade-off. He would provide for their needs as long as they didn't challenge his authority, anad they wouldn't challenge him as long as their needs were met. If nothing else, he would care for them because he would have no one to rule over if he hurt the citizens, and then he would go back to being ignored and powerless. It doesn't make sense that he'd allow that to happen, especially after taking such drastic measures to rule.
Interesting question. Before the revelation of his true colours, he seemed capable, responsible, and determined. However, his dark side could easily cause problems too.
I can imagine him starting off as a good king, but after some time has passed he may begin to get greedy and selfish and mistreat his people. I think he'd just deteriorate over the years as he becomes Mehr and Mehr used to his power.
I don't think he would make the best king, since he was going to kill someone to get power, and I do think he would mistreat the people of Arendelle. But I think he would make sure to be just good enough so that people outside of Arendelle would think he was a great king. Therefore, the people of Arendelle wouldn't be living horrible lives, just not so great ones. (Okay, now I'm just rambling like an old professor. :D okay, here's my imitation.) Ahem. In conclusion, Hans would not be a great king, but he wouldn't be the worst. It just depends on how Du look at it. But I'd say he wouldn't good. Especially if I was in Arendelle.