Fine tuning and balancing your game is a tough one, how much of the players experience should be a matter of luck vs the players skill? In this GDC talk Elias will teach you how to balance your game in regards of luck and skill.
AnyDice.com is a tool to help you visualize your dice probabilities.
If you are using the Unreal Engine you can read their documentation on Distributions here.
For unity unless you want to implement it yourself there are a few assets for randomness and weighted random.