If you haven't played this game before, I highly suggest doing classical. Tactician is not....a good time investment, bc they have not balanced it and is very poor. Would not recommend until it is changed.
As for what to pair, if you want to go the mage route, you can pair with Geomancer. With Geo you get Poison dart, which you can use on yourself for heal since you're going undead. Geo gets poison, slows and physical armor buffs, so its pretty good to spec into, even if you're gonna make one of your other companions a dedicated caster. The other caster can just spec into Hydro and that will take care of your magic armor stuff.