Expansion vs Node Addition

Hi,

We have following use case

> Currently we are on single node , BI 4.1 SP4

> Need to move to cluster and BI 4.1 Sp6

> FIle store size 3.5 TB ( we are having short time to clean the content , as old system is having lot of issues )

Thinking of following sequence , please provide me more inputs around it 

New Cluster > 2 Application nodes -tomcat

                       2 Intelligent nodes  -

                      2 Porcessing nodes

Installation: 1. Installing node 3 - BI SP4

                    2. Installing Node1 - Tomcat 7

                    3. Migrating the content from old system

                    4. Updating Node with BI SP6

                    5. expanding the installation  for node 4,5,6

                    6. installing tomcat on node 2

                    7. Clustering and configurations

For #5  what do you suggest , just prep the nodes and install expand mode and add to cluster or separately install BO on each node and add to the cluster

Any inputs will be really appreciated

Thanks

Badri