How do I interpret OmniDiskSweeper's file size information and delete unwanted files?

Those are very, very small files. Don't think that's what's causing the fan to speed up.

Look for files that say gB or hundreds of mB to release space.

Space usage does not impact heat and by extension fan speed.

Heat is caused by the CPU doing a lot of stuff. Check running processes and background tasks in Activity Monitor rather than disk usage for that.

Run the third party app EtreCheck and post the complete report here so we can examine it for possible clues. Your issues are more likely due to an issue with third party software or a hardware issue and this report will help to identify those issues.

How to use the Add Text Feature When Posting an EtreCheck Report - Apple Community

OmniDiskSweeper and similar apps are only meant to allow users to easily locate large folders & files. Besides small files are not going to make a difference. Plus, the only files that you should be moving or deleting are the ones you have created and or downloaded....they should all be located in your Desktop, Documents, and Downloads folders. Some apps may hide some files within the hidden Library folder of your home user folder....again, these would be files you created or downloaded.