From whatswithjeff.com: "One of the most common questions ask by a consumer/user before buying or upgrading their PC/Desktop or Laptop is “how much memory do I need for my PC or Laptop?” “Should I get a 4GB, 8GB, 16GB of RAM or even higher? Before you go off buying a memory or upgrading your system below are some guides or tips when it comes to how much RAM or memory do you really need for your computer this 2013?"
What is better Ryzen or Intel? Choosing a processor for a PC can be a daunting task, especially if you're new to computing.
The ThinkStation P360 Ultra is a tiny beast.
2-4Gb if your an every day/ office user
8Gb if your a Gamer
16Gb+ if your working with maya, video editting etc...
As much as you can afford to get. The more you have the better off you are.
There is no such thing as "too much" RAM...