1. The 'rehabilitation period' for an offence is defined by law. It can't be reduced.
2. CRB checks are only currently available to employers only when the work involves contact with vulnerable people (or to information about them) or in certain other areas (such as work with the police or security services). Most employers can't insist upon a CRB check.
3. Since your conviction would show up on ANY CRB check, there's no particular reason to worry about an enhanced check. (Enhanced checks show exactly the same information as standard checks, plus any additional information that a senior police officer, or other relevant professional, deems relevant. So, in your circumstances, there would be no difference between what might appear on a standard check or an enhanced one).
4. With very few exceptions (such as the ban on people with convictions for sexual offences against children working in schools) there are no automatic bans on people with criminal convictions working in any particular type of employment. Over a third of British males acquire a criminal record before their 30th birthday, so employers will often disregard irrelevant convictions.
Chris