USB-C cards don’t consume extra power so if you want to minimize drain then use only C. Of course this comes with usability drawbacks.
Yes, Windows will automatically switch to hibernate after 5% of the battery has drained during standby.
Yes, though the difference isn’t that huge.
The drawback of hibernate is that it takes longer to get back to where you started (~10 seconds) vs 1-2s with modern standby.