SEPM on VM

We are going to migrate 11.x to 12.x. on an enviorenment  here are some quaries:

       1.SEPM installed n Xen server, what sould be the system configuration of SEPM server for managing 2500 SEP clients ?
        

       2.SCCM(System center configurution manager) is running on the environment. What is the file extention( patch/exe or others) of client upgrading/migrating command from SEPM to clients. Will it support/work throgh SCCM?
        

       3. Replication of SEPM activated there. What is the types of SEPM replication (active-active or active-passive or else)?

       4. Is it possible to transfer SEPM from XEN server to vmware or converting XEN server to VMware ?