If you apply for a JAR Licence, it will expire in five years & you will have to pay to renew it, at which point you would be given an EASA licence.
Your CAA licence & ratings will convert directly to an EASA licence; the requirements for going from CAA-->EASA are identical to the CAA-->JAR requirements, so there's really no advantage to the JAR route. The
CAA's handy guide has the details, p19.
I think you will need to have valid ratings before applying for an EASA licence.