OAB from 2003 to 2010 in coexistence mode

I am working on a 2003 migration to Exchange 2010. The deployment assistance now recommends to move the OAB's from 2003 to 2010. I have already created a Web-based OAB on a 2010 server. I have 5 2003 Exchange Servers and they all have a 2003 OAB. Two are in the Netherlands, the others in France and Germany

Question:

1. Do I need that many OAB's?
2. Do I need to move the 2003 OAB's to 2010 when I already have a 2010 web-based OAB?
3. And if I need to move them, do I need to move them all, or is one sufficient?

Thanks in advance for your help again!

Olaf