Hard to say without knowing the guest operating systems' requirements regarding CPU, memory, disk I/O and throughput. With the 2TB disks you mentioned - which I assume are S-ATA disks - I'd guess that the limiting factor will be disk throughput. Disk capacity is easy to calculate (keep in mind that there's some overhead) and you can run up to about 30-35 VMs. For memory subtract ~4GB for the ESXi host, so without overcommitting memory you can run at least 14VMs. The CPU performance will most likely be sufficient for the number of VMs you can run with the other limitations I mentioned.
André