When you choose a package from mintInstall, click on the "More Info" button. This will give you a thumbnail of the package, the repo it is in, the installed version (if any), and the latest available version.
A meta package is an installer package that gathers all required files and dependencies to install a major package (such as KDE 4 or Gnome) into one place for easier installation. Once the package is installed the meta package can generally be deleted without harm.
The mintInstall software Manager is not set up to be configured in the way you want. If you open Synaptic Package Manager, you can use "Settings=>Preferences" and Settings=>Filters" to set things up any way you wish
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