Without knowing the specifics of your PC it's hard to say what to work on. In general, and particularly with PPCC, having a powerful CPU with many cores is the biggest bang for the buck. In my case I went with an Intel i-7 5820K 6-core CPU as it was overclockable but not ridiculous in price. The base clock is 3.3GHz which boosts to about 3.7GHz without OCing and I've increased this to 4.3GHz.
The GPU is important for handling effects but isn't nearly as important as the CPU. I opted for an EVGA GTX 980 Ti Hybrid that's near the top of the line and is water cooled but I find that it isn't working as hard as I figured it would. When running 'Valley Benchmark' the temp of the GPU can hit 52C, but even during a long render session the max temp I see from the GPU is about 35C so I'd say it's probably not working much beyond 50%.
Having a lot of RAM is helpful though not 100% necessary. I have 32GB which I'd argue is the sweet spot unless you go for a much more expensive PC. Going with less than 16GB is not advised. The speed of the RAM is not nearly as important as the quantity.
Finally, the HD or SSD you use during edit and render can make a difference but as I mentioned before there is the issue of file transfer from main storage to working storage. What would be nice is a more seamless method for handling files within PP. What would be nice is a file setup script that lets you define the files from main storage, the drive/folder for working storage, and if and how you want to work with proxies. With such a setup PP could handle the file movements automatically.
Brian