I have been using Ubuntu for the past few years and I've finally caved and decided to try to dual-boot Windows 7 with Ubuntu 16.04. But, everything says to install Windows first then Ubuntu with it.
I don't want to wipe it and put on Windows the Ubuntu, as I do have some stuff on it. It's all easily replaceable, but I just want to take as little time as possible.
I don't know if it will help, but I have a second storage drive formatted as NTFS.
Installing Windows on an Ubuntu system will delete or corrupt GRUB bootloader. If installing Windows successfully removes GRUB; Windows bootloader can't boot Ubuntu so only Windows will be accessible then. But if installing Windows just deletes/corrupts GRUB files, GRUB will boot into recovery mode and you won't be able to access Ubuntu or Windows.
However if you really have to install Windows on an Ubuntu system- first prepare a Ubuntu live CD/DVD/USB flash drive, install WIndows. Then follow this is a tutorial to reinstall/repair GRUB so that you can access both OS.
