[quote=@Light]
If you want to go more lenient and flavorful this way, I think I will add in more graviturgy for my astrologer to start. Would certain aspects of cosmic magic like time travel still be forbidden? Perhaps the rulings on these are more about particular uses and spells rather than entire forms of magic.

Sure, drawing the life-force out of your classmates is I'll advised, but what about calling a spirit to ask it questions about the past? I'd rule both as necromancy but one is clearly harmless.
[/quote]

Gravity-based effects are fine, but I would be cautious with grandiose uses of time travel. Regardless of the rules meta-side, in the actual in-RP universe, I would still think time travel would be closely monitored. However, instead of saying "no, you can't do that," I think a better idea would be to have in-RP forces respond in kind if certain thresholds are violated XD. So, in other words, if you wanted to have your character go back in time to change an outcome of something, chances are something akin to Time Wraiths would soon be on their trail XD. Perhaps we can have a Professor who specializes in time-related spells who can teach them how to use mild time-travel that doesn't get flagged, and then it will be up to the character whether or not they abide by that or try to go farther and see what happens XD. 

As for what would be considered "acceptable," we can just say that short-distance time travel - say, within 24 hours of your current time - creates sort of like a temporal personal pocket dimension. Basically, that lets you go up to 24 hours into the past to try out different missed opportunities or go up to 24 hours into the future to see possible outcomes, but it has no effect on the actual, "live" timeline. And we can say it has a geographical sphere that extends out five miles in every direction from your initial location. So, that gives one a free reign 48 hour, ten mile bubble to hop back and forth to their heart's content. If they get too close to the edge of the bubble - or try to go beyond that 24 hour window in either direction - they will begin to feel resistance, like a rapidly thickening fog. If they choose to push past that, then the bubble breaks, and it becomes real time-travel, triggering the attention of the Time Wraiths. 

As for what the Wraiths are, no one knows for sure, but legend says they are the lost souls of people from previous timelines who broke their bubbles and were forced by the gods to defend the current and future timelines for all eternity. But do the Time Wraiths actually exist? Anyone who was suspected of having encountered them never returned, so how can they really know? The teachers claim they are real, but it is up to the students whether or not to believe them XD. 

As for your final question, I would say the Professors frown upon recalling spirits from the dead because interrupting their afterlife is not only extremely rude, but could probably open a path for other forces to follow them through from the other side. Again, you can try it and we'll see how the universe responds ;). That being said, we can probably have ghosts of past Professors who have agreed in advance to be summoned to help students. The living professor who handles that class - probably Arcane History - could give each student a handheld crystal ball to summon and communicate with the dead, but with strict instructions on who they can contact and when.