Is there a way to view thumbnails on the lightbox widget before clicking on it? The idea is to make users understand that this is a whole gallery and not a single picture.
Not sure I fully understand your question, but have you noticed you can link lightboxes? So you can have multiple thumbs on the page, and each of them link to the same kightbox, with all the high res images for these thumbnails. Check the lightbox widget settings in the settings panel.
This is exactly what I had in mind. I know about this option. But I wish it came more straightforward, with no need to tinker with creating all those thumbnail boxes manually.