Glad that you got the adjustment layer issue worked out. Not quite enough info to troubleshoot the other problems. The following page outlines the kind of info that helps zero in on the cause of such problems: FAQ: What information should I provide when asking a question on this forum?
As to the cache files and rendered previews, you do not need to keep them. Premiere will regenerate them as needed. Because re-conforming the audio and re-rendering the sequence takes time, you probably want to keep those files around for the current project--unless, of course, you have reason to think that the cache or render files are causing problems.
To keep things clean and get the attention of more people, it would probably be best to start a new thread for the other issues.
