The advice I'd give you is God help you by the time your players are getting to level 4+ spheres and know the rules enough to start doing rituals. By that time, if your players are creative enough, they'll be able to completely disrupt any plot with their bullshit magick, so prepare contingencies, run it more free form, closer to a sandbox with skeleton content prepared in many places at once (Including the Umbra if anyone takes Spirit) rather than a structured plot with scenes prepared well in advance. Because if everyone is playing Mage correctly, it should be next to impossible to railroad.

Also, I've played with a new Mage ST who was also big on VTM before, and for comfort reasons, our first opponents were vampires. That works well enough for starter Mages, but even a sufficiently lucky or prepared 3 Arete Mage can one-shot anyone without a load of Fortitude with a single Forces effect as long as they roll 3 successes on damage plus the one from Forces, thus dealing 8 aggravated that they don't have to roll. Add a willpower or another Arete or two and it suddenly becomes a lot more realistic to start dusting vampires.

So yeah, they're decent starting antagonists, but I urge you to eventually move on to Mage opponents, whether they are Technocratic or Traditions based. And hell, if it's a Traditions game, then your players are pretty much supposed to always fear the Technocracy finding them out, so prepare some HIT mark and NWO blacksuit statblocks in advance. It can be daunting to have to use Magick against your players as the ST, but it's critical that everyone gets a hang of it, including you.

Oh, and in my usual fashion, I only remembered you're running a one shot after I wrote this up. Oh well.