ThinkSystem NVIDIA Quadro P4000 8GB PCIe Active GPU

Please help if this GPU is supported by Hashcat as this GPU supports OpenCL API and apparently it should be supported.

Also how much Hard Disk and RAM we should be looking to support that password cracking infra.

Is 2 x 3GB RAM and 2 x TB HDD is enough to run this?
AFAIK, every GPU which has an OpenCL implementation is supported by Hashcat.

You should have RAM >= VRAM in general, so 2 x 3 GB are not sufficient. I suppose this a typo and you meant 4 GB anyways, which would be fine then. There are no hard requirements concerning hard drives, but if you plan using dictionaries, an SSD shortens the load time. The required space solely depends on the size of the files you are using for cracking, e.g. dictionries, hash lists, etc.