Sharing Whimsyshire crafting materials between difficulties
Solution 1:
The only restrictions are these:
- The materials are account bound so they cannot be traded or sold on the auction house
- The materials can only be used to craft the Staff of Herding for Normal difficulty. Crafting the higher grade staves requires that you have the Staff of Herding from the previous difficulty + the plans for the upgraded variant, which can be bought during Act 4 of the difficulty in question.
With this in mind, you should be fine crafting the staff with ingredients taken from multiple characters or difficulties.