Upgrading an undersized vCenter server

A vCenter server for a small farm (4 hosts and about 200 VM) was originally installed on on undersized hardware and now must be moved to a more appropiate host.

I see two options, implementing a dedicate host or a virtual appliance.

• If I select a dedicated phisical host and perform the procedure described on page http://kb.vmware.com/kb/5850444, how much RAM should I implement, given the same host must act either as vCente and Update Manager? Based on the documentation I would say 4 GB, but based on my experience I am not sute 4 GB are enough: can anybody please suggest the right memory sizing?
  
• If I select a virtual appliance, can I migrate the cuttent vCenter from the currend physical host to the virtual appliance?
  
  • Given I can migrate the current vCenter to a virtual appliance, what are the disadvantages of implementing a virtual appliance instead of a physical host?
    

• As a very last chance, can I instead use VMware converter to convert the current vCenter to a VM and install it inside the vSphere infrastructure?
  

Regards

marius