1. Please check “Enable customer registration on the “My account” page” option in Woocommerce > Settings > Accounts > Customer registration.
To enable FB registration go to Theme Options > General > Facebook Login > fill in all the necessary fields. Read more – https://xstore.helpscoutdocs.com/article/87-facebook-login
2. Yes, you can use this image.
3. Please add this code in Theme Options > Styling > Custom css: