Species is most easily defined in extant sexual populations, since you can observe reproductive compatibility. Two populations that cannot or will not breed are considered separate species. Just in the last few months I've noticed that most creationists have punted on claiming that this does not occur, quietly moving the goalpost for macroevolution to the genus level. That WHAT does not occur? Reproductive compatibility?
Yours is the classic definition of "species." That answers #3 above. On this, there is no dispute.
Loss of reproductive compatibility. Speciation. We used to fill up thread upon thread with creationists arguing that speciation does not occur.
The bar has quietly slid up, perhaps because the evidence for ring species has percolated into the creationist community.
These retreats and bar-movings are not advertised or acknowledged. They ripple out as one listens to or reads another, much as various arguments have their fashion. (Just now, the platypus is in on FR. Gold chains in coal and trilobites-in-a-human-sandal-print are out. But come back next month.)