[Samba] Samba4... upgrade member servers?

[Tim]

I am upgrading a samba 3 domain controller with an ldap backend to samba 4 via 
classicupgrade and was wondering... do I need to upgrade our samba 3 file 
server at the same time or will it continue to work as is for the time being?

Also, I have read conflicting opinions about whether I need to run winbindd on 
the member server (we do currently) given our use of ldap. Could someone 
enlighten me please? :-)

Thanks much!
Tim