Quick take: Nikon’s free basic plan includes 2GB of storage, but Nikon camera owners can access up to 20GB of free storage in the company’s Image Space service. (Both options accept photos only.) There are no paid storage tiers. Those who own certain Nikon cameras, such as the D7100 and D5600, can also store an unlimited number of photos, scaled down to 2MB, using the Nikon SnapBridge app.
If you have a Google account, you also have 15GB of free cloud storage on Drive that never expires. What you choose to back up is obviously up to you, but Drive works particularly well with documents, allowing real-time collaboration and editing in plain text, spreadsheets, and presentations. Emails and other files received through Gmail will count against your storage, but keeping your inbox under control can keep more of the complimentary 15GB of storage open for use.
The TLS protocol prevents man-in-the-middle attacks from succeeding, while encryption secures your data in transit and at rest. Private encryption prevents anyone other than you from reading your files. The drawback is that services which provide it won’t be able to reset your password if you forget it. To avoid losing access to your content use a password manager.