Intel and Nvidia? You should probably decide onto that too. Btw, check this website https://pcpartpicker.com/products/motherboard/#f=8
Yup, I'm familiar with PCPartPicker. I can easily go in there and mix and match parts, but was hoping for guidance. Pros and cons for certain parts or manufacturers. Like, I'm reading that an Intel CPU with Quicksync would likely be ideal for Plex transcoding so I'll probably do that. But do I need a discreet GPU as well, or would the iGPU be good enough?
Integrated GPU is great. It might also depend on how many concurrent clients you want to serve. And, you then dive into extra variability according to codecs in your library. I have no experience with Plex, but this info might be helpful to you anyway, check https://jellyfin.org/docs/general/administration/hardware-selection/#graphics-cards-gpus