Social niceties v roll initiative

The ill-assorted group of Lost City adventurers are currently gathered in the Emir's palace and getting to know each other through some judicious roleplay. Shortly they will be trekking across the desert in the company of handmaiden/bodyguard Madrissa.  At this point they will be subject to the whims of the dice. 

I'm always slightly conflicted about how to start long-term campaigns.  Given the usual PbP timescale, we'll be with this for around 18-20 months and not everyone will make it all the way through.  Life will intervene.  It always does.  That said, the vast majority of this group are long-term players in my games and well aware of what they're getting into.  The attrition rate may be low,  which I'd like.  Storytelling is much easier with a consistent group.  However you cut it, a PbP campaign is a long haul for players and GMs alike

So how to start one? 

1.  Start in media res.  The "roll initiative" approach.  Launch the players into an immediate battle.  This has some charm.  You get an immediate feel for how the battles will run and the players get to make some early dice rolls.  In the flurry of the first few days of posting, when relentless screen refreshing is the norm, combat goes really fast.  Nobody will hold back from posting in combat.

The downside?  Hurling players directly into a combat lets them show what their characters can do, not what the party can do.  They don't know each other.  The battle may well be unsatisfying because they haven't yet had time to get a sense of each others capabilities.  I've said before, and repeat here, that 4e heavily rewards teamwork and synergy.  In media res goes against that.  Yes, they can read the character sheets, but that's complex and not as organic feeling as getting a sense of who is likely to need the flanking bonus, who can heal you out of trouble and who needs to stay firmly at the back because you know who these people are.

2.  Build up slowly, setting a scene and allowing some story to evolve.  In general, this is my slight preference, but success depends on the players.  With my drama professional head talking, I know only too well how hard it can be to roleplay cold.  Players in the early stages of a game are polite and slightly tentative.  They are often reluctant to thread hog and wait for others to respond.  It is up to the GM to prod a little and make sure questions are asked that need some sort of response.  You have to provide a world to interact with.  More work than rustling up a battlemap and a set of monsters, but generally more worthwhile in the long run.

In this case, I'm taking option 2.  As I said, most of these players are known to me and I to them.  Some trust has been built up and I will work to move them on fast if things seem to be sticking.  We'll get to the dice rolling soon though.  They, and I, need to know what these characters can do.