Ability to set default dates and date limits for custom date fields

In a custom form I want to calculate the default date for custom date fields using $$TODAY or dates on the object. (Planned Start, Planned Completion, Etc.)

For example DE:Project Launch Date might default Project Completion Date - 1 month to allow projects with post-launch activities, but would still be editable by the user.

Ideally a date field should have default date, minimum date and maximum date all calculated to allow us to sanity check our users.

So DE:Project Launch Date would default to -1 month of completion but must fall between entry date and planned completion date.

And a DE:Delivery Date must be after $$TODAY+3d