Hi Wai -
Sounds like a fun exercise! There are a lot of firms that do this kind of work (full disclosure - mine, included). As the data architecture across both instances is quite different, there are some things you'll want to consider as you move forward.
My firm, Tellenger Inc., does this kind of work and has experience doing many CRM conversions. The hardest part is the data mapping plan and the relationship linking which is probably where you would need the most help. We'd be happy to do an introductory call with you if you are interested in learning more.
Heatherc: 240-731-3535e: email@example.com
ECHO might be a great fit! ECHO is based in San Francisco, we have offices in Europe as well.
Below is a quick summary of ECHO's Salesforce services:
We will be at NTEN. Visit us at Booth 456Best,