The installer will (should) find the EFI partition and create a directory there for the grub code. /boot/efi will be a separate mount.
Install as normal - grub itself will install under /boot/grub (probably - I don't use Debian). Should be nothing for you to do to get the setup you want - however all UEFI implentations are vendor specific.
Regardless, it shouldn't affect your Win system.
Edit: - looks like
this might be useful if you get into trouble.