Yup, you can get a 16GB Kit here as that is what I have in my 3020 SFF.  For the processor, if there is not much difference in price, you can also consider the 4590 or 4690. You can even go i7 if you'd like with the 4770 or 4790. You can also consider an SSD upgrade as well, as 500 GB SSDs and bracket are dirt cheap. (less than $40) 
Hello, I am interested to see if 1333 mHz 16 GB of RAM would work in an Optiplex 3020 SFF. My current setup is: System Type x64-based PC BIOS Version/Date Dell Inc. A20, 5/27/2019 System Information screenshot: [IMAGE]  
Upgrading an Optiplex 3020 SFF to 16 GB of RAM.