Help with Gravity forms wordpress plugin

General information for the website: Selling insurance
Description of requirements/features: We are using Woocommerce with a single produce and Gravity Forms to collect information on the Product Page.

We need some help with doing the following.

The Policy we sell is available in 8 differernt options
Europe 7 Day Cover
Europe 14 Day Cover
Europe 30 Day Cover
Europe 365 Day Cover

AND

Rest of World 7 Day Cover
Rest of World 14 Day Cover
Rest of World 30 Day Cover
Rest of World 365 Day Cover

These are selected on a drop down in Gravity Forms.

The purchaser also selects a START DATE for the policy.

We need some JS in the Gravity Form that Grabs the START DATE of the policy and ADDS the number of days COVER to give us and END DATE to the policy which populates a non-editable form field on the form.

We then also need a unique policy number to be generated. The form also collects a mobile - the policy number could be the mobile number (with no spaces) and the END DATE of the policy. For example. 5555555555-17-11-2014
Extra notes: The current form can be seen here (dev site)

http://assist24.toastmt.com/product/family-assist/