These kind of questions get asked every week and here's the thing... it's all about
your expectations of performance.
Illustrator will work great on 8GB - to a point. What are you doing with Illustrator? How complex and large are your project files? Is this for educational/hobby or professional use?
What other software would you be using at the same time?
If you demand best performance and/or time is money, then you might get a little bit frustrated with 8GB on more complex projects. I certainly recommend 16GB for
anyone buying a computer who has the budget for it, but 8GB is still just fine for most usages.
Keep in mind you've come to a computer enthusiast forum - you're going to see a lot of posts here by people who study the frame rate of the the UI animations or consider a 2 second "hiccup" while switching between application windows the same as having their finger nails pulled out.