1) Treat the singers as humans
2) Be friendly, because nobody likes to work under the baton of scary conductors. It's good to be authoritative occasionally, and by "authoritative" i mean strict.
3)Argument? That's actually quite unlikely to happen, if you're a good conductor, and if they're really ethical musicians lol.
4) Complaining about passages is good because it identifies the problem. Solve it with them and don't forget to ask them about their opinions as well. It's making music as a group together!
All the best!