The only restriction of note is no fast mana. This cube has no budget restriction, no inherent complexity restriction, and no restriction on where cards are printed (i.e. supplemental sets and Universes Beyond). Singleton is broken, but only for Fetch Lands (x2) and Shock Lands (x3).
Cards in this cube are selected for both individual power and flexibility. Most cards should fit in most decks, and no card should require any specific card(s) to function.
Cards at the upper tier of power should not repeadetly generate advantage alone; they should require setup or ongoing support to maximise their effects.
It should also be noted that the cube has more lands than the median at ~80. This means over 1/5 of the cube is land.
I was drawn to a low curve for two reasons:
Power - By having the peak of the curve lower, it is inherently more difficult for an individual card to overtake the entire game, by virtue of merely being cast.
Agency - By having the average cost of cards be lower, the average number of game actions players can take is higher at most points of the game.
Lands - By increasing the number of lands in the cube, the number of unplayed cards in the average player pool decreases. This ultimately adds additional meaningful decision points to the draft.
My philosophy was heavily inspired by @andymangold and his (co-hosted) podcast Lucky Paper Radio.
A lot of advice offered and questions answered by @Alveric and his cube list Alatta.