Can my clients still create image selections, comment on images and so on when entering the gallery in presentation mode?

The Presentation Mode is used for pure presentation and download of your pictures.
If you want to give your clients more functions, you can activate the "Allow switch to edit mode" function in your "Gallery Settings".
If this point is active, your clients can switch to the usual mode by clicking a button on the top right corner of their gallery.
Entering the edit mode they will find all the practical functions of picdrop.
All gallery settings you've set will apply here.
With just one click, your clients can return to the presentation mode at any time if they wish to do so.