Can we make Custom Fields apply to some Custom Item Types but not others?

This would aid greatly in reducing confusion by our end users. Some examples: 

• We have a Risk custom task type. We would like to have our Risk-related custom fields (Risk Impact, Risk Probability, Risk Mgt Strategy) to apply only to that item type. We don't want these fields available to any of our other task item types (including default/core item types).
• We have item types to represent sub-projects (e.g. Epic, Work Package, Phase, etc.). There are custom fields like Customer, Strategic Goal, etc. that we'd like to apply only to our top-level project item types but not the sub-project types to reduce inadvertent filling by engineers.

If we could make certain custom fields required by some item types, that would be even better. We're having a lot of trouble getting folks to adopt request forms, so in-item required fields before closing the item info pane would help even more.