For the gallery class you can see everything here: https://github.com/hyunsupul/aesop-core/blob/master/public/includes/components/component-gallery.php
And for the admin settings: https://github.com/hyunsupul/aesop-core/blob/master/public/includes/components/component-gallery.php
Forthe options that are available in each gallery you can go here: https://github.com/hyunsupul/aesop-core/blob/master/admin/includes/components/component-gallery.php#L223-L310 and add the lightbox option you want included in the grid gallery as seen in the photoset gallery.
b) change what field value is used for the caption
What field value are you wanting to use?