Vision demo is around 250GB minimum, spread over two VMs. I'd plan on 400GB+ to be safe, allowing for some snapshot space.
It might be possible to fit it into 8GB RAM, but you wouldn't like it. Go for 16GB. Vision runs well enough on four total cores but six would be nice. That said, spend on RAM and faster drives (definitely SSDs) before spending on more cores. Definitely go for high IOPS disk - SSDs are great.
I assume that you are planning to run the VM version of the demo? I've done it on an eight core VM server using a four-core DB VM and a four-core App VM with virtual drives built on top of two striped SSD drives. I didn't bother with pass-through because I really wanted the ability to easily take snapshots. Performance was surprisingly good.