High Fantasy Mysteries

Waaay before. Algorithms to crack substitution cyphers around 700?

Yup. Look at the authors and check the play testers in a few of the ArM5 supplements. Bard is a really good storyteller and has the mathematical skills to deal with issues arising with a complex system well. E.g. He's the one who caught the oddity in how Minor v. Major Magical Focus were written and how improving could make your scores go down with one of them (Minor, I think, but I may remember wrong.). Despite his talent and skill, it's a lot of work for a couple to write an RPG on the side while dealing with everything else.

Ah yes, that seems about right.

My suggestions:

  1. For planar travel read Amber RPG or if you have the time or The Chronicles of Amber by Roger Zelazny. I'm sure it will be high inspirational to your work.

  2. Looney tunes actually has one of the most usefull "magic" I has see, The Portable Hole

  3. Mysteries can be well developed as Intéllego magic mechanics since in a high magic scenario you can do all kinds of investigative magic: Raise the dead witness, read suspect minds, bust liars, divinate crimes before they are commited, speak with stones, animals, plants (lots of witness huh?), see waht happened in the past, magically decode cryptography, etc

In my campaign, I used the Tree of Life from Kabbalah to map the various dimension you could travel. Each of the Kabbalah world was aligned with one Realm (most were magic/fae, with only one representing Hell and another one the Divine).
Of course using the Kabbalah as the source of the dimensions map has its own implication in term of which religion is the closest to God but otherwise, it was a neat way to use historical material to blend in Mythic world.