Hi,

For the first query there are a couple of helpful posts

https://supportforums.cisco.com/discussion/12367366/vss-vs-stackwise-vs-vpc

https://supportforums.cisco.com/discussion/12502831/what-functional-difference-between-vss-and-vpc-nexus

Regarding the second query, vPC can be enabled across all major Nexus platforms like 5000, 7000, 9000 series. You can reference the config guides for the specific models like the one below

http://www.cisco.com/c/dam/en/us/td/docs/switches/datacenter/sw/design/vpc_design/vpc_best_practices_design_guide.pdf

Manish