George
Thanks for the reply.
Positive: Deleting the preview files will free up a lot of free space. Consideration: if you open a project that generated one of those preview files to get the best possible preview of that file on the Timeline playback in the Edit area monitor, you will need to Timeline render that file again to get another preview file and the best possible preview. This is only a previewing matter and will not affect export. This Timeline rendering will not fix but will alert you ahead of time what to expect and direct you as to whether or not you need to work on the Timeline some more before export.
Please let me know if you are OK with the above information. I will clarify further if you want.
Your progress sounds good.
Best wishes.
ATR