Opportunity approval workflow

When using an opportunity pipeline it would be good to be able to have an approval workflow.

The approval workflow should alert the approver and request their approval under three circumstances:

The value of the opportunity is above a certain amount.

The opportunity is set to a status that is flagged as requiring an approval.

The opportunity is above a certain amount and is set to a status that requires an approval for opportunities above a certain amount.

The approver should receive an email with a link to the opportunity and they should be able to approve or decline the opportunity.

If an opportunity is declined the owner is then able to update the opportunity and send it back for approval or close the opportunity.

If the approver approves the opportunity it should then go to the next stage.

The opportunity owner should not be able to edit the opportunity while it is awaiting approval.