for labs, checkout these linksBayu Wibowo | VCIX6-DCV/NV
Author of VMware NSX Cookbook http://bit.ly/NSXCookbook
https://nz.linkedin.com/in/bayupw | twitter @bayupw
The actual VMs deployed in the lab will depend on what you want to demo...
The minimum you need will be NSX Manager appliance and at least one controller (Which is deployed from within vCenter once NSX Manager is registered with it). In production, the only supported configuration are three controllers but for lab/demo; one will be fine (Unsupported).
Then it depends on what you do from there… You can deploy multiple Edges and Logical Routers (DLR) or none depending on your use case. Each Edge or DLR will be a new appliance deployed.
The system requirements are well documented by VMware but there are also a number of blogs for home labs where people have tweaked the memory/cpu to reduce the resource footprint if that is a requirement (Unsupported).
If you want to get to grips with NSX (..even use for demos) and also its requirements outside of a technical paper/KB article I would suggest you sign up for and use http://labs.hol.vmware.com/
Hope this helps,