big Premiere project with many clips - is it better to storyboard on paper first?
Storyboard first, then shoot, then edit.  A storyboard is a tool for organizing your thoughts before you even pick up a camera.  It's like a script, and usually follows from a script, but gives you a better idea of where to place and move the camera.  This is called "shot blocking".  

The shotgun method of gathering footage with the hope of being able to string it together into a coherent story is a mistake made by many beginners.  There's nothing wrong with gathering lots of footage.  In cases like documentary work, it's often necessary.  But even when you shoot this way, you need to have an idea of what you're looking for, and how it's going to fit within your story before you sit down to edit.

As for the 40 hours of footage you already have, I'd say no, don't worry about drawing it out on paper now.  I guess you could use a whiteboard if that helps you organize your thoughts, but really you've got what you've got, and you're just going to be duplicating your effort when you sit down at premiere.

It's difficult for a one man operation to compartmentalize the processes to make good video, but you should look to the film industry for guidance.  After all, they have billions of man-hours of experience.  They've got it whittled down to a science.  Directors, cinematographers, gaffers, grips, editors, colorists, producers, writers, and everyone else you see in the credits all have their own job for very good reasons.  When you're trying to do it all yourself, it's best to wear one hat at a time.