[Linux-cluster] Xen / Redhat cluster : 5.3 to 5.4 upgrade question and best practice

[F M]

Hello,
I need to upgrade a Xen cluster using RH servers from 5.3 to 5.4.

It is a 3 nodes cluster (+qdisk) and 1 luci server for management.

All VM are in a GFS2 FS in /home/domU/FQDN folders.

Each FQDN folder contains :
-The xen config file
-the VM FQDN.img  file

I read about some issues with rgmanager from 5.4 (unable to create VM config files that were not in /etc/xen). This bug has been fixed in rgmanager-2.0.52-1.el5_4.1
Can I safely apply the update without modifying any config made with 5.3 ? Do I need to tweak the cluster.conf between 5.3 and 5.4 ?

Also, 
Is it better to upgrade the luci server before the nodes ?

I am also curious about the nodes, what is the best practice : moving VM , removing the node from the cluster, upgrading and then reboot, see if everything is fine and go for the next one after that ? Can I stay with a mix of 5.3 and 5.4 for several days ?

Regards,

F