Hello,
1) I would recommend you to synchronize translations.
Make sure you placed translation files of the theme into the /wp-content/languages/themes/ folder with correct names (language name and xstore theme suffix, e.g xstore-de_DE.po, xstore-de_DE.mo).
Button Sync (Loco Translate plugin http://prntscr.com/glemdq) allows you to synchronize your translation file with pot file. Then you will be able to translate untranslated strings.
2, 4, 5) Please read the documentation of WooCommerce, or contact the support of the plugin.
3) Appearance > Customize > WooCommerce > Checkout.
Regards