just be aware that all of your data will be on the card including your photos and other files. this also means that your phone will be reading and writing as you use your phone. this will thus increase the wear and tear of your sd card......so make sure you are using a good quality card or you run the risk of the card getting corrupted and thus you will lose everything on it.....so make sure you backup things regularly.
Backup photos to Google photos - should be automatic if you have automatic backup/restore to Google turned on. Anyway you can use one of the backup apps in the play store, or just connect to your computer via USB or Bluetooth.