For your Plex storage upgrade, considering your need for 5 or more bays, the DS1821+ or DS1522+ from Synology could be excellent choices. These NAS systems offer robust performance and ample storage expansion options, ensuring they meet your needs not just now but also in the future. As for hard drives, sticking with Toshiba NAS drives like the ones you already have is a reliable choice for consistency and compatibility. However, if you're open to other brands, WD Red and Seagate IronWolf drives are also popular options known for their reliability in NAS environments. Remember, compatibility is key, so always ensure the drives you choose are compatible with your chosen NAS model.
https://nascompares.com/nas-builder/
https://nascompares.com/nas-builder/