I don't know what happens after TNG, but I'm curious about some tidbits in this topic.
- How did the Romulans gain access to Borg technology? What of Federation?
By now everyone has a little bit of Borg tech. The Fed has Seven of Nine working in the Daystrum institute. How the Romulans got it too isn't explained but I'd guess through a mixture of spying and salvaging battle sights.
- What happened to the Borgs?
At the end of Voyager they were cut off from Federation Space when the Voy destroyed their transit system. They're probably still rebuilding it.
- What is Android B-4 and how can Data still be alive after what happened in Nemesis? The "evil copy" did not have Data's memories or personality.
B4 is the droid from Nemesis. During the film, Data transfers a copy of his memory into the machine in order for b4 to learn how to be a "person." It doesn't work at first. But in the final scene of Nem, Data's memories begin to surface and b4 begins humming the song Data sung at the wedding. Sometime later, La Forge upgrades B4's positronic brain to the same level as Data's, causing the Data personality to surface and be reborn. This info comes from the Star Trek Online history entries which according to CBS is canon, and since CBS own Star Trek this is the way it is.
- How the hell is Spock even still alive? How old do Vulcans live?
A few hundred years. Hell both him and his dad appeared in Next Generation... even humans get a sweet health care package in star trek. Doctor McCoy lived long enough to appear in the TNG pilot, and Archer from Enterprise was an Admiral in Star Trek 09. But yeah, Vulcans live a damn long time, so do Klingons for that matter.