Uh, its a secret
Yes, you need to have Prime. Actually, there is a hidden "Labs" menu option which you can activate to enable additional "beta" features.
Once you are in Nova Settings menu, press'n'hold volume down button for a few secs. Right under neath of Backup and Import option you will see a new entree for "Labs". Holding volume up will disable it. In there you will get some new options including Big Grid Size Options. Once you select it and go back to Desktop setting - now you can have a grid with up to 16x16 size
You can go crazy with that stuff because it scales down all the icons. I found 8x8 to be manageable and very useful for fine tuning the placement of icons/widgets, as well as resizing.
Now, all I'm hoping for is that in the next update they will add an option for dock background. I have no idea why it's not available yet. I had it in my ancient Launcher Pro 2 years ago.