60,000 is the minimum for statehood. American development would easily hit this by the current date.
Legally, it's the minimum for statehood. Realistically, it's far too small.
Alaska is not a fair comparison. When it reached statehood, it was pretty close in population. In 1960, shortly after statehood, it had 228k as opposed to Nevada's 288k.
Using Alaska as a model is good here. If you look at its population growth, a couple of driving forces were the military bases and oil. Presumably the Homestead Act had some effect, and presumably Greenland would get an exception similar to Alaska's when Homesteading came to an end.
The purchase of Greenland would take place after WW2, which is when most of Alaska's military bases were built. This cuts down on the immediate hot war need for bases. Greenland is certainly going to have a few military bases, especially with the pressure of the cold war... But I don't think it'd have as many as Alaska many. It has a strategic location for bases, but honestly, how many would the state would need? We have a base on Greenland as is, and the permanent population is only a couple hundred. I think we can assume that the population would be higher if this was American soil, but if we want to go into a population of ten thousand? That's two orders of magnitude, a pretty big change. Greenland has a very strategic location, but primarily for monitoring, rather than having a huge actual presence. Alaska is much better situated for big military bases.
For oil, we can look at natural resources of Greenland. And... until recently, there's pretty much nothing but fish. Some mining and drilling prospects have been found in the last few years, but even if we assume America will push that date a few years earlier, it's not going to make that much of a difference in five years or so.
Even with homesteading... Most of Greenland is really
awful for living. It's a good size on paper, but I don't really see too many people headed over trying to set up a plot. There are much better cheap places to live.
A few small military towns, maybe a six digit population, but still not large enough for statehood to be realistic. And I don't know how much the native Inuit/Danish population would be for statehood. We can assume most of the people who move to service military towns would be for statehood, but they'd face staunch resistance from the tens of thousands (a significant number in this case) of people who identify as Danes (probably English speaking by 2010 but certainly not "American" any more than a typical Guamanian is).