I have backed up all of my .apk files to my laptop. Can I delete the .apks in the Amazon venezia cache folder without detriment and be able to put them back on the sd card and reinstall from there at a later date, if I want to?
You can redownload them any time you want or just install them using a file manager, no need to put them back there.
If you backup them to your PC it's a good idea to use something like this to keep track of the various apks.
Once the apps have been installed the APKs in the cache folder are completely worthless. Even more so if you've backed them up.