

7200RPM drives are fast enough for most applications, though you may run into issues streaming 4K (or higher) resolution video.
This is highly unlikely as even the highest bitrate 4k content is going to cap out at around 12MB/s while spinning drives can transfer at 120MB/s per drive. I’d say that 99% of people hosting their own media servers are still solely relying on spinning disks for storage as SSDs are still extremely expensive per TB comparatively and don’t really offer any advantages for storing bulk media at this point.
No. Keep all the software running on SSDs while using HDDs for storing the video files themselves. You’ll never max their transfer speed out especially considering you’re not sharing with friends and family.