For moon gems, here is my rule. Every treasure hoard has 1 moon gem. The first four moon gems you (you the entire party sharing the gem) you roll 1d4, from the fifth one on you roll 1d6 (one die is rolled for the entire party together). Maxing out the roll gives you a major milestone with a power up, rolling one under the max (i.e. five on a d6) gives you a major milestone without a power up.

Then if that roll failed, and if anyone is trailing behind in moon gems (maybe because they've missed sessions or even died and started over), that subset of the party (anyone not at max moon gems) get a reroll attempt that only applies to them, giving them a chance to catch up.

If the hoard is in a location that is way under the party's moon gem count, it's a d10 instead. (Like going after goblins when you are level ten in D&D.)

This is how the moon gems work their magic to bring power to brave adventurers good or evil.

This moon gem system is for this setting only, not a general rule for all Fate. I.e. it's more a house rule for CBCH specifically.