5/6 Bay, Capable of Transcoding 4K Files via Plex, M.2 Slots to Use as Storage Volumes?

[namiry]

Looking for a NAS to use at home to stream content to 1-2 MacBook Pros, 1-2 iPhones, and/or a 4K TV (LG). Would likely only have 1-2 streams at a time. Content ranges from 720 to 4K. Will also use the NAS as wireless backup via Time Machine for the two MacBook Pros. Knowing that I'll be using hardware transcoding (plan to subscribe to Plex Pass), I want to find a NAS that allows me to use an M.2 NVME SSD as a storage volume with PCIe Gen 3 capability (either with an expansion card or natively with slots), with the idea that I'd run Plex on that NVME volume and use it as a transcoding directory as well. QNAP allows M.2 volumes to be used as storage, so this should work on a QNAP device that has the right hardware. A few questions:
1. Is this overkill for my use case?
2. If it is overkill, which NAS from either QNAP or Synology would be best for the transcoding use case without the M.2 NVMEs as storage volumes?
3. If it is not overkill, which QNAP devices with PCI Gen 3 M.2 slots would work for the transcoding use case?
4. Can an iPhone or MacBook Pro direct-stream 4K content from a NAS?
Thanks!