I'm wondering, is there an optimal dungeon/mythical beast order, where each zone around that dungeon scales in difficulty, or is every zone around the beasts pretty much the same difficulty, making the dungeons be truly doable in any order?
Since the game is entirely open world, they're all fairly balanced. The order I did was Zora, Gerudo, Rito, and lastly Goron.
Doing Gerudo first may have some benefits because of the jeweler who gives elemental resist circlets, but this is not necessary as Rito and Goron gear are much better (and have a set bonus).
Doing the Zora one first could have advantages because the power you get is an auto-revive, which can help quite a bit.
Doing the Rito one first would help you travel a bit more, given that the power you get helps a bit with exploration.
In particular, the Goron one I would save for last. You'll need money or patience to get around Death Mountain (given the heat that sets you literally on fire), and it would probably be the toughest of all of them to do first. But, you certainly could.