How many managed Servers do you need?

Hi,

One thing that has come up time and time again, is when trying to think about a
new project and a new WL domain, is trying to know how many WL Managed Servers
do you need?
Does BEA have some sort of metrics which says ok for this amount of input we
recommend you having 4 managed servers on 4 single boxes?

And is there think on have 2 managed servers on 1 box or 2 managed servers on
two boxes? 

Any Help Appreciated.

Kind Regards,