1 - 2 or 3 Clusters?

Greetings,

I have a question about sizing or the shape of my cluster. I would appreciate some best practice and real life input.

General layout of equipment:

• Server 2012 R2 Data Center
• 12 HP DL 380 Gen 9 Serevers with about 160 GB RAM each
• HP 3PAR SAN with 35 TB of storage setup with iSCSI
• 2 Cisco 4500 switches to provide redundant 10 GB fiber iSCSI connection to servers
• System Center VMM 
• 3 Older Gen 6-7-8 HP servers as replication servers connected to a HP MSA storage SAN

I currently have 7 servers in 1 cluster and then it hit me like a brick....

1. Do I add all 12 servers to one cluster? 
2. Do I make 2 x 6 node clusters?
3. Do I make 3 x 4 node clusters?

I look forward to hearing some experienced and seasoned veterans weigh in on this.

Thank you,

Eric