Adobe Premiere Pro / After Effects Hard Drive Scratch Disk and Cache set up in temporary situation.
Personally, I would ditch the usb3 drive for editing. Assuming you can't buy a third drive I would do your setup like this. 

Do a two drive setup.
C: OS and media cache
d: (raid) Media, projects, previews and exports.

I've always followed the advice here and its worked great for me.

https://forums.adobe.com/servlet/JiveServlet/showImage/2-2906955-31395/Guideline+Disks.jpg