Given your requirements for photo storage, remote editing, occasional Plex usage, and cloud backups, along with your budget and concerns about drive selection, I would recommend considering the Asustor Flashstor FS6706T or FS6712X. These models offer ample storage capacity, with the FS6706T accommodating up to six drives and the FS6712X supporting up to twelve drives, providing scalability for your expanding photo collection. While there may be some limitations with Asustor NAS compared to Synology, they offer competitive features and performance. Additionally, their compatibility with third-party apps can enhance functionality, including AI photo tools for easier searching. Keep an eye out for any upcoming replacement models, but in the meantime, the FS6706T or FS6712X should meet your needs effectively within your specified budget.
https://nascompares.com/nas-builder/
https://nascompares.com/nas-builder/