What are the best practices for SharePoint server 2013 at VM hardware level?
basically it depends about the one's requirement. How many users you are expecting, what service application will be used, purpose of the farm etc. here are some hardware requirement:
Type Memory Processor Dev/stage/test server 8GB RAM 4 CPU All-in-one Database/Web/Service Application 24GB RAM 4 CPU Web/SA server 12GB RAM 4 CPU DB server (medium environments) 16GB RAM 8 CPU DB server (small environments) 8GB RAM 4 CPU
Here is really good article from Technet, which will cover all topics in it.