In CM 5.1 configuration, presence server 1.0 software is shown as included. Do i need to order another MCS if i want to install presence server. And what else do i need to use 10-15 unified personal communicator?
yes you need a new MCS.
Normally you get the PAK for the Presence Server licence in the software box.
To add 10 Personal Communicator client, you'll need to order 10 CUPC licences. Moreover, you'll need 10 Device Unit Licences to Activate the Presence for the 10 Personal Communicator clients.
Finally, if you want to use Personal Communicator as a Softphone, you'll need 3 Device Licence Unit for each client.
To be clear, for each Personal Communicator client, you need:
1 CUPC Licence
1 DUL for Presence
3 DUL for Softphone (if you use it).