No, the catalog file is not backed up to the cloud, it can only be backed up to a hard disk (although from there you could use third-party programs to back it up to the cloud). The presets and templates are not backed up to the cloud. While a version of your photos may exist in the Adobe Creative Cloud, I would not consider that a backup, it's not the original photo.
If you are going to wipe out your existing Windows 8 installation, I'd make sure you have backups of at least your catalog file(s) and all photos and presets, the full list is here: Which Lightroom files do I need to back up? By the way, I wouldn't bother making backups of your previews, these will be recreated when you restore everything and launch Lightroom.