The railroad is scheduled to be down for at least a year. They haven't given a definite end date. Along with it they will be draining the Rivers of America, which means that sailing ship Columbia, Mark Twain, canoes, and Tom Sawyer island will be closed as well. The reason for all of these closures is that they will be changing the current path of the rivers, and the current path of the railroad, to make room for Star Wars Land. The land is going to take over the current location of Big Thunder Ranch, as well as some backlot/offices that currently sit behind the scenes in that area. There have been many rumors of it taking over parts of Toontown as well, but that has not been confirmed.
I don't know about Disney purchasing a plot of land, all I can think of is a recent purchase of a plot across the street on which a hotel stands currently, but it would be nowhere large enough for a whole land. Maybe someone else knows more about the purchase you reference.
When the river and train reopen they will follow a new route, though the stations will remain the same.