Need Advice With Rebuilding My Old PC

I recently built a new PC and decided to turn my old PC into an ITX build. Here is a link to my old PC's build: https://pcpartpicker.com/list/8CTRwg

I plan on keeping the GPU and hopefully the storage, but I know I'll probably have to upgrade the CPU+Mobo and get some new things and that's fine, I just don't want it to be so expensive. I'd also love to build it with the Fractal Terra ITX case.

It doesn't have to be a high end build, aiming more towards mid level (although I'd also like to see a high end build) I'm really aiming to just play League of Legends, Warframe, and Black Desert on a secondary PC.