Adding 2008 R2 server to 2003 domain:  2003 DC to 2008 R2 DC

Thank you in advance.  I am prepping some 2003 AD dc’s before adding 2008 R2 servers to the domain.  Obviously I will need to run adprep on the dc’s before, but wanted to confirm adprep /forestprep and adprep /domainprep.  We have 3 domains, parent and 2 child domains.  The parent Domain DC has all the roles including the schema master and the child domains only have pdc, rid and infrastructure.  It is a while since I have done anything with domains so wanted to run this by someone with more experience/knowledge.

I was going to run Adprep32  /forestprep on the Parent domain (which holds the schema master)
then run Adprep32  /domainprep on each of the child domains
Should I also consider running  /gpprep on the child domains?

Does this sound like the correct route?  The other thing is I don’t envisage actually setting up a 2008 r2 server to control the parent domain for a short while as it is one of the child domains I am more concerned with at the moment .  Can 2008 DC’s sit happily in a child domain when there is no 2008 server in the parent domain (I presume it would be ok if the forest, domain and gpprep went successfully)?  Also can i only run 2k8 r2 server in a RODC mode?

As I said many thanks.

Leon