Can Android Device Manager only locate your phone if it is signed in to your Google Account?
To use Android Device Manager (ADM):


  Your device's location access need to be turned on and be signed in to your Google Account. Android Device Manager won't work for devices that are turned off or that don't have a mobile data or Wi-Fi connection.


No, you will not be able to retrieve photos remotely from your phone. You can check whether your photos were uploaded by default to Google Storage. To prevent from losing photos in the future, you can setup your phone to automatically upload photos to the cloud.