You can upload a disk image for notarization and staple a ticket to it. The ticket covers all the contents of the dmg. You can't currently staple a ticket to a zip file.
Someone else is looking into answering the questions about SDK version and unsigned kexts.
Currently, due to changes in macOS 10.8.3 (see bottom), you'll need to distribute two installers, one for macOS 10.8.2 and earlier that contains the unsigned kext as unsigned kexts cannot be notarize and one that is notarized that contains the signed kext for macOS 10.8.3 and later.
The kext installer for macOS 10.8.3 or later that is meant to be notarized will also need to be linked against the macOS 10.9 SDK or later, although you can set the deployment target to macOS 10.8 to get compatibility for macOS 10.8.3.
Alternatively, you can separate them into an unnotarized macOS 10.7.5 to macOS 10.8.5 installer and one notarized installer for macOS 10.9 and later, if it's easier to demarcate the downloads that way.