hi peter, i've done this before and it's very easy (and done it the other way around).

just leave the registration plates on, the system is completely different to germany. there is such a thing called 'trade plates', but you will not be able to get them as you do not have a registered place of business here, and anyway they do not cover travel outside of the UK.

for insurance purposes, your insurer should just insure it against the VIN

the V5 document has a section to fill in to tell the dvla that it has been exported. the previous keeper can do that, but make sure you get a receipt for buying it. as you probably know, you can download one in both english and german from ADAC.

any other questions, do not hesitate to ask