Semi-Random Image Gallery (w/ Fancybox)

I’m using fancybox (of Kingsize Theme) to display a random image gallery on the home page of a site.

I would like the gallery to

1. Select a limited number of images (from post attachments, or a folder) for each page load.
2. Always display certain specified images.

Ideally there would be a place in the media manager to select which images would always be displayed, but for now it could work to just add the individual image IDs to the code.

Am suspecting that the code recommended here would be a good starting point.

Any insight much appreciated.