Hi Kagiso,
That server should be fine for testing purposes. For Production, you'd probably need to look at pumping up the memory, and making sure that the disk you have is fast (SAS is great!) and has redundancy (you mention 1TB, but not if that's total disk space, or simply a single disk).
You can refer to the DLP 15.5 System Requirements Guide on the link below. It will outline everything you need in order to implement your 3-tier setup:
https://support.symantec.com/us/en/article.doc10602.html
However, if this is for testing purposes, you would probably look at providing 4GB per VM and a minimum of 2 x vCPUs per VM. You don't mention the CPU in that ProLiant either.
Once you are happy with the testing phase, you should refer to the sizing guide which will give you the requirements to get it running optimally:
https://support.symantec.com/us/en/article.doc8253.html
Thanks!