1) SlimDrivers only allows you to download and install a single driver. DriverUpdate is the premium version that allows you to download and install all at once.
2) We recommend leaving the installer packages in place because it makes uninstallation easier. However, you can always use the restore function so it is not absolutely necessary.
3) The forum for SlimDrivers is HERE. Post in the appropriate sub-forum that is related to your question.
Hope this helps.