Where did they come from? Probably from a settlement that was south of their entry point. This allow for the carving of traveling "round the West". It could also be a idiomatic expression for anything other than a coastal area, which is quite likely.
Was this part of Erlindsson's mission to find the lost Norsemen? Probably not. The lack of reference to a King or reign would lead me to the conclusion that the trip was a single month long lark, a simple trip to learn more about Vinland.
The absence of thirty men from a settlement is somewhat difficult to understand. If the area of settlement was extremely rich in food resources (which is quite possible considering the stunning salmon runs up Canadian rivers at the time) it would certainly be possible. The other possiblity is that the settlement was large enough to be relatively unaffected by the absence of this many men. Although a large settlement has not been found that would be this size, it may exist in some protected place that has not been found. My own opinion is that the area required substantially less work for survival and that the men's absence would not be missed for a fairly long period of time. Perhaps that was why it was called Vinland.
Could ten men sail an ocean going ship? Yes, indeed. Because of the simplicity of the rigging, it could probably be sailed by 4 people. 1 forward watch, 1 on the lee board (steering) and 2 on the mains'l.
This is the big Cormorant Lake just west of Detroit Lakes, Minn-- not the other Cormorant Lake in Grant County just a few miles NW of the stone...