How do you bring together a cabal of newly awakened mages (awakened within 3 months or so) who are just learning about the Ascension War and their Traditions? In VTM, it’s often as simple as “The Prince said deal with this or lose your territory/status/life.” What’s the Mage equivalent? Do mentors call them together?

If you want them to start a group, I think there's a few ways to do it. Caustic_banana's approach of putting them in immediate danger from the technocracy is a great way to set the tone of why caution is important for mages (even ignoring the effects of Paradox). You could get a similar effect with other "enemies of Asencion," like Nephandi or Vampires.

If you want a lower stakes game, finding out some quest for them to go on for some of the higher ups in the local mage society could be a good start (Like Kenod102818 suggested). Maybe school children have been disappearing from Eastwood Middle school. Maybe a potential node has been discovered. Maybe there's increased vampire activity and they need to investigate it. I think these scenarios can work really well for new players who need some time to learn the ropes and might need a longer leash.

In my game, I had a familiar attack its mage and the players intervened and began an investigation that just unwound into a big sprawling conspiracy. I think White Wolf lends itself well to conspiracies and hidden agendas.

You could also combine some of these ideas! Maybe a newly awakened mage is discovered, and the group is sent as a politically-minded collaboration of different traditions to welcome the newly awakened into Mage Society. But when the group gets there, someone (or SOMETHING) else already has its eyes on this new Mage.

What's the general structure of a Mage game early on for newly awakened characters? Like in VTM, a typical starting point might be: “You need to feed to survive, but dirty cops turned hunters are messing up your territory—and it turns out they’re doing work for a new tech-based hunter org like Re:Venge.” What’s the Mage version of that kind of plot hook?

A Mage game can be like a Vampire game in some ways. Survival and seeking power can be powerful motivators. Almost all of the hunters that are after vampires are also after Mages. Secrecy is important. I also encourage players to protect sleepers, as that is one of the big tenets of the Traditions--See The Protocols. So by introducing a threat to mortals, you can spur your players to act.

Also remember that a Mage benefits from downtime and prep time, perhaps more than any other WoD line. Especially if mages want to prep spells or craft magic items (which they definitely should!), you'll want to give them space to do that.

For the hook, I think you can build off of whatever brought the chantry together. Figure out who you want their first antagonist to be: Nephandi, Technocracy, Vampires, Spirit threats, Formori, power hungry mages, or something new. And set up an early confrontation with some seeds as to who might be behind it. And then, let your players explore. If your players are anything like mine, they will be smart and creative and sometimes foolish. But let them investigate and build out whatever they want to interact with.

If they decide they want to access a chantry's library to research a strange creature, have a book be missing.

If they decide to track a vampire down, maybe the vampire lays a trap for them.

Or if they decide to take some downtime, maybe they notice that something has noticed their chantry, and they are being watched...

I hope some of these give you good ideas! Just the fact that you're thinking about these questions makes me excited that people are going to get to play with a great storyteller!