Unity is the 17th episode of Season 3.
The third episode of season 7
Q2, episode 19, season 7.
Last season, last episode.
series 4
Friendship One, Season 7
In Season 4, episode 1: Scorpion (part 2)
Tom Paris is reinstated as Lieutenant Junior Grade in the episode "Unimatrix Zero" (season 6 episode 26).
Yes, Ted Levine appeared in "Star Trek: Voyager." He played the character Captain Harkins in the episode titled "The Chute," which is the 12th episode of the third season. Harkins is a Starfleet officer who interacts with the main characters as they deal with a challenging situation in a penal facility.
Star Trek Voyager - 1995 Unity 3-17 was released on: USA: 12 February 1997 Germany: 14 August 1998
No, David Hyde Pierce did not play a Borg on Star Trek Voyager according to his bio on the Internet Movie Database. The episode in question is episode 96 from season 5, called 'Drone'. The Borg drone was actually played by J. Paul Boehmer. Interestingly, J. Paul Boehmer also appeared in an episode of Frasier.
Yes, the very last episode.
The episode in question is from Season 3 and is called "Displaced". It was first aired May, 7 1997.