No version of Pages is a Word clone, and Apple offers no apology, or guarantee that exporting (translation) to Word is entirely accurate, or even intelligible to CreateSpace. So yes, using Word would eliminate any mystique from Pages, and CreateSpace may find the document more compliant with its input expectations.
What part of the following two paragraphs did or did not occur in those three failed attempts to download LibreOffice?
When you download LIbreOffice from their site, it will go directly into your Downloads folder. I have never had it fail to download. If you click on the Dock icon next to your Trash, that is an alias for your Downloads folder, and it will show a list of recently downloaded files. The file at the bottom is the last download. Click once on LibreOffice_5.1.3_MacOS_x86-64.dmg, and the installer will open on your Desktop. Drag and drop LibreOffice into the Applications folder. Eject the LibreOffice Installer icon from your Desktop.
Open a Finder window, locate your /Applications folder, and the single LibreOffice icon. Right-click on it to open it, and choose the Open button. Because it did not come from the OS X App Store, the operating system will put up a brief progress bar to verify the application. It will pose another dialog box ... just click that Open button, and LibreOffice will launch. You only have to go through that ritual once, and afterwards, the application will launch normally.