This actually came up in IRC this very week and we got some actual numbers! Whoop!
So lets start with size:
"Right now, we're looking at around 256 km across. We may go bigger than that if we can." - Good Caspian
However, when the questions started flying about if that was the whole, world, first continent etc. Caspian became his normal helpful self:
"Well, when the game first starts, is there a difference between the whole world and the continent? ;-) ... You have no idea how big And you shouldn't." - Evil Caspian
How fast will we move across it though? Because if we all move 100km a second that will not matter! Well luckily we were provided those too. Waling is 1.44m/s, 3.8m/s for running, and finally 7.2m/s would be a sprint.
That means if you ran constantly, which you can not do because you have to rest, and went in a straight line, which you almost certainly can't do because of terrain etc., then it would take almost 19 real life hours to cross. You add in the time for rests, navigation, dealing with issues on the road, then it is going to take a while.
Basically, please, please make a shipping company we need you!