I have low bandwith so cant download much would it be okay to backup drivers and (even if old) install them whenever buying a new gpu, will they update by themselves or will they be stuck on the version i downloaded (nvidia)?
If you buy a new card it will come with a disc that will have a newer version of the drivers. Then whenever you can get on Nvidia.com and get the latest and greatest.
You will be stuck with that version that you downloaded. Sure you can download and keep the installer but it will be outdated once a new version is released.