I'm split on this too, just because it might take the same amount of time to 5 man to 14 as it would to solo. The thinking behind it is "after I get my first character to 10 the starting area should be a bit more manageable so each character after that should be quicker.

However, it's still going to be launch night and I think it's going to be nuts for at least 30-40 hours so we might aswell do 5 right away.

I'm leaning towards 5 but we'll see.