No need to insure the bike to do a first registration using the V55/5 forum, unless you are in Northern Ireland - no idea why they have different rules. You will need a dating letter and MOT, NOVA reference number/letter. I assume you have the original Japanese registration certificate, you need to send the original off to the DVLA. If you dont have that you will never be able to get a V5. If everything is in order it will take about a week to get the V5.