If your photo library is as extensive as you say, it is likely growing in terms of storage requirements as well. Given that, I'd opt for a 4 bay drive minimum. You can start with 2 drives and add more as your storage needs grow. In my opinion, 2 drive devices limit you.
Personally Asustor is my go to. The hardware is fantastic, support (if needed) is amazing, and they just, well, work!!! But Synology is a go option as well. I personally have had poor results from QNAP, however, that was over 3 years ago, and they may have gotten better. But my primary choice is Asustor.
Well damn, sounds like the DS423+ is the way to go. I agree about the bay count. I also really like the access to everything they offer incase I need it.
If you haven't already I'd check out NASCompares on YouTube, some great videos on Synology and NAS's in general. He also has a very detailed series of setup videos for Synology which I am slowly working through when I get time.
Edit - Sorry @jkudave , just realised the clip you linked was from NASCompares....
Probably not. Storage itself isn't a complicated task and isn't to hard on even a low end CPU. It is really about the capacity you need and just keep the devices cool for reliability. CPU on a NAS is really dependent on what you plan to do to push it.
I have the Asustor AS5202T. It costs $299. It comes with 2gb ram, but it can be upgraded to 8 gb. It has RAID capability and you can install up to 2 x 18 TB drives. Although you can use standard desktop drives, it is recommended that you use drives designed for NAS usage like Seagaste Ironwolf. The device comes with three USB 3 port that can be used to add extra storage, either as flash drives or USB hard drives or SSDs.
Connectivity is via two 2.5gbe ports that can be combined for 5 gbe to insure rapid file transfers if your LAN allows.
Another nice feature is a HDMI port that can be connected to a monitor or flat screen TV for viewing of photos and videos or playback of music.
Asustor also makes drives with NVME slots if you require rapid access, but that is not normally required for photo storage.
Not really a NAS, but the WD My Cloud works great for phone photo backups.
Easy for people to add the app to their phones and it's also easy to deploy off-site for added safety.
I use qnap.. recommend the ts264 (2 bay) with say 16-20tb drives in raid 1. if you need more storage get a 4 bay unit in raid 5
Also, see if you can get the earlier ts253d or ts453d or even the older ts453be or ts253be i have all of them in various locations.
It gets pricy with good nas drives ,, as you know.. i perfer seagate ironwolf or ironwolf pro (they are worth it with 3-5 yr warranties as drives die when in use 24/7)
For photo backup these are real nice as you can set them up to automatically backup just by plugging in a cable to your camera or phone or snap in the sd card.