CPU: Which is more important: instruction-per-clock or multiple threads? If multiple threads, then how many is the absolute maximum that Shotcut can utilize? GPU: Nvidia CUDA or AMD OpenCL? Professional or gaming card? Which should be powerful enough? How much VRAM is adequate? If you just say OpenGL, then AMD should be a terrible choice. RAM: it is covered in the useless “minimum system requirements”: 4 GB for SD, 8 GB for HD, and 16 GB for 4K. At least it is the only thing useful.
FIY: I intend to build a PC with Xeon L5420 + GeForce GT 630 + 8GiB DDR2 for my cousin to do some amateur editings. I know such hardware is old, but he needs something cheap but still does the job. I focus on preview performance over render performance. The videos are usually short, thus smooth preview is more important.
The Zeon should work well. 8 GB RAM is adequate, but you can never have too much for a video editor. The GT630 - for a budget card I use and recommend a GT710 or GT730. They support GPU export of H.264 video which exports much faster than a CPU. To get GPU support for H.265 you will have go a bit higher/newer. There is a topic here on this forum with a table listing nVidia GPUs and what they support. You will have to search for it.
-=Ken=-