The third episode of season 7
Q2, episode 19, season 7.
Last season, last episode.
series 4
Friendship One, Season 7
Tom Paris and B'Elanna Torres get married between scenes in the episode "Drive".
Tom Paris is reinstated as Lieutenant Junior Grade in the episode "Unimatrix Zero" (season 6 episode 26).
No.
Yes, the very last episode.
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.
Ashes to Ashes S6/09
Endgame Part 2
The same as every episode of Voyager: Robert Picardo