You would probably have fun building a hard magic system. Hard magic being a system that has strict rules for how things work. Soft magic being Gandalf style where how it works and how it's limited is unknown.
One thing I've been thinking about recently is conservation rules. are there any popular fiction worlds that explore conservation of e.g. magic? The only example I presently know about is https://www.hpmor.com/chapter/78 (search for "conservation").
Most authors will sacrifice some amount of "realism" in the interests of story-telling (compared to Yudkowsy with HPMOR at least). A couple of Magic examples come to mind:
* Brandon Sanderson does a lot of Magic impacting Physics. The magic is often proper unexplained magic - but it's impact on Physics is pretty well modeled. In the most recent Mistborn book - there's a remark that explains that when the character magically reduces their weight while flying through the air - their velocity increases. I think Brandon points to that - but says that he loves the consequences at that level - getting to the point of red-shift/blue-shift for bubbles of fast/slow time is story breaking. See also his laws of magic: https://www.brandonsanderson.com/sandersons-first-law/
* Pat Rothfuss in the Kingkiller chronicles has a magic called "Sympathy" where rule 3 is "The law of conservation".
Although "unknown magic" and "ancient powers" are convenient, it bothers me to think there's no consistent system underneath it.
In the setting of the world, people in the world can view it as unknown, but the author is the god and should have a decent idea of how everything works.
