No, each source gallery does not need to be on a separate page. You can put all separate source galleries on a single page and link to them using their Section IDs or Section Anchor IDs (if you use a Gallery section) or Block IDs (if you use a Gallery block). For more details, you can refer to this post about IDs configuration.

No, currently you cannot use Lightboxify URLs in a gallery that has the lightbox feature enabled. If you include Lightboxify URLs in a lightbox-enabled gallery, they will be treated as normal links. For more information, you can refer to the Lightboxify URLs FAQ.