It is (I'm sure you know) important that your file-naming convention be rigorously applied (you are using it to encode information; where it is not rigorously applied it will be difficult and perhaps impossible to correctly decode the information). You might set up a manual validation system before import. Name Mangler is a program I use and recommend. It handles tens and even hundreds of thousands of rewrites with aplomb.
If your images are currently grouped in Finder folders, you should look into importing using "File→Import Folders as Projects".
Keywords are just text tags applied to records in the image database. Aperture comes with built-in Keywording tools. Custom metadata fields allow for multi-line text input. I create a custom "Comments" field in all of my Aperture Libraries. You may find something like that useful in one way or another.