I think the main intent in going to 4e was to reduce the sheer number of options 3.5 had. It was versitile, yes, but also very confusing for new players, and they wanted new blood.
Anyway, to each their own! Both systems have their merits.
Ensou: You've got it right. You're bound to get lots of questions in the ads--some people just skim over them before posting interest--so the more clear you are the easier it'll be for you.
As for posting expetations, I mean how you want player's posts to look, and how often they should post. It's not neccessary to lay it out, but it's helpful.
For example, I've adopted a common MW rule for my game that says players should post at least every other day; this keeps things moving a long at a decent pace without leaving players behind. If a player doesn't post in a full week without letting anyone know there will be a delay, they risk getting booted from the game. If you're clear about this from the start, you have something to fall back on with players who don't post much at all and hold up the game. Of course, your posting rate can be as slow at once a week without hurting anything, it's all preference.
You may also want to outline other things. Some common MW guidelines are:
-each player should post their speech in a different colour to distinguish from one another.
-spoken text is in bold, while internal thoughts are italic.
-Insert a stat block with each post during an encounter to the DM can easily track action points, hit points, powers used, etc.
-How much narative you expect there to be in player's posts; eg. in this game you want more explanation on what the attack looks like than just "My guy hits the bad guy with his sword and he falls."
Again, none of that is strictly necessary, but it does let your players know from the get go what you expect.