Is Hashicorp's Vault suitable for personal projects as well? The Vault documentation indicates that there is a master key and that multiple keys are required to access the secrets, but does this mean that Vault is not suitable for personal projects if there is only one PC?
Vault will distribute multiple unseal keys but there's nothing to stop you from keeping all of the keys in one place for a personal project.

The one time I did it I set the keys to 3 and kept them in different physical locations along with online locations.