See Duplicate and Copy to for all blocks.
There’s isn’t a save and reuse to dedicated storage that isn’t on-page; and yes, one way of working is to copy existing pages and edit from there.
Headers are edited on your Home page. You can have multiple headers and set the conditions for when each of them is visible on other pages.
Search these forums for ‘headers’ to also learn more from other users’ experiences of them, features and any limitations. For example