Is the BeeStation Plus worth it over the 4TB BeeStation?

Yes if you want double the space and the faster processor. Synology rates the Plus at roughly 2.6x faster phone backups and 4.8x faster desktop sync, which matters as your photo library grows.

Does it protect my data if the drive fails?

No. It has a single drive slot and no RAID, so a failure loses the volume. Keep a copy on an external USB drive or another backup target.

How much RAM does it have?

The BeeStation Plus ships with 4GB of DDR4 RAM. Some listings mention 8GB, but the Plus model is specified at 4GB and Synology does not position it as user-upgradable.

Can several people use it at once?

Yes. You can create separate accounts with their own private space and shared folders, and the quad-core CPU with 4GB RAM is sized for family or small-team use.

Can I expand storage later?

You can attach an external drive over USB-C for extra space or backups, but there is no second internal bay, so the 8TB volume is fixed.

Does it replace Google Photos or iCloud?

It can take over photo and file storage and remove subscription limits, but you lose the cloud provider's off-site copy, so plan a separate off-site backup.