2 Very basic questions from a rank beginner

[Leo]

@Kiwiwolf

First off is thumbnail size. I set the size I'd like for the thumbnails in my lister, then save that lister as default. However when I shut down and restart, the thumbnail size is back to original. What am I doing wrong and how can I set my preferred size as my default.

You can set the default size under Preferences / File Display Modes / Thumbnails.

@Kiwiwolf

The second question I have is how do I dispense with the need to have the file extension showing in the file name? For example instead of The Godfather.mp4 I'd like to be able to use just The Godfather. Is this possible in Directory Opus and if so how do I make use of this feature?

From the lister, go to Folder > Folder Options and then the Display tab. There there is a checkbox, Hide file extension in Filename column.

See Folder Formats: Quick Guide for how to make that the default for all folders.