It sounds like everyone agrees on the frequency of posts.Usually that's how that goes, yes : the GM points out what would be usual or proper, everyone agrees on it, and then that's how it goes, with the GM managing with that time frame to let all the players answer to the events of the game. The usual expected posting frequency is about one per day, but it's usually slower. Which makes me think : whatever frequency you and your players agree on, you should expect it to go slower in reality, simply because the frequency is only as strong as the weakest link, in part, and because real life takes precedence (it should), every time.
What about the length of each GM post? Really depends on your GMing and prose styles, but I'd say that generally, you need to describe as much as you would out loud at the game table before letting the players place one. It's more important here because they can't interrupt you on the spot. So you need to be mindful of that fact, and manage your posts to let the players intervene when you think their choices or role playing makes a difference.
I will usually write a few paragraphs or lines of dialog before letting the players react. You should check out the current Ptolus threads,
like Davin's introduction thread, for instance, to see how that goes.
How much information is the GM expected to give, how much player actions is he supposed to assume, before handing it off to the players? You should be very careful to let the players be themselves and make their own choices which impact the way the game unfolds, here (see above). If you skip over too much, players will feel frustrated because they wanted to react to this or that but you fast-forwarded them in time in the same post. If you do it too much, they'll get frustrated because they'll feel like the game's stalling. It's a question of finding a sweet spot where everyone feels like they have a meaningful input on the way the game unfolds, and stuff keeps happening nonetheless.
Also, how are rolls generally handled (does the GM make the rolls or is it an honor system)?I have a few ways of handling it : one is the dice roller (like
Invisible Castle), second is to just let players and myself make their dice rolls themselves physically and trust them to not cheat giving the results (obviously not something you want to do with everyone, especially if players don't know each other, because perceptions matter more than actual cheating in this, here), and finally me GM making the rolls physically for everyone.
I usually roll as GM with what the players think is best. In the Ptolus game, this means we use invisible castle. In my World of Darkness game, that means I make all the rolls myself.