I really like the dice system for this! My only request would be more guidance on when Enhancements should come into play. You give a lot of ways to enhance a roll but no examples of when they should be applied or how they might actually impact a roll in terms of effectiveness or feel.

Great question! Enhancements, as mentioned would come in the form of anything from upgraded or magical equipment to potions, boons, etc. I left it vague since the possibility of what could be considered as an "enhancement."

As for the when. The answer is when it's applicable. If a character gets a pair of "Boots of Leaping" they get a +1 whenever they try to jump across a long distance, or a significant height.

If they drank a "Potion of Durability" then for whatever duration you, the DM, put on that potion that player takes -1 damage from attacks made against them.

Or, perhaps they simply upgrade their starter sword to a really cool Buster sword (nonmagical but still super cool). They might get +1 dice when rolling attacks using it.

In addition to this idea of "enhancements" it also works for the concept of leveling up. Although this is meant for a one-shot you could always play a longer game where players can level up simply receiving+1 dice which they can use for any/every roll moving forward. They've grown and developed and become stronger.