Re: What exactly is...
the function of the small computer station along the rail behind the Captain/First Officer chairs? I don't recall it ever used before the arrival of Seven, but she seem to use it exclusively thereafter. Is it some kind of specialized Borg interface made just for her? Another sort of science station (which would make poor Harry even more useless)?
Kim's station was the Ops position, so another science station wouldn't necessarily affect his bridge duties. The console you're referring to is an auxiliary tactical and operations console that could be used in addition to the posts normally manned by Tuvok and Kim, but not necessarily in lieu of them.
"He clapped his captain—his friend—on the shoulder. Yes, this man was very much like James Kirk, in all the ways that mattered." --Christopher L. Bennett-- Star Trek: Mere Anarachy, The Darkness Drops Again