Combat: I think you should do ALL the initiative rolls for us, as this will speed up play immensely, because we will not have to wait for everyone to come online once just to roll ini.
I'm wondering whether you want us to act in ini order or whether you'd prefer to adopt group initiative. Many play-by-posts use group initiative (i.e. average ini modifier for party, one roll vs. average for monsters), which has the benefit that people can post when they are online and don't have to wait until another one has posted their action. From my experience, I'd say group ini is a fine thing, as it saves 1-3 days per combat round, but I'm fine with either way.
Other rolls: Is a mix ok, i.e. is it ok if I do some of the rolls myself and let you do others?