1. Not sure what example your referring to about the examples but the enlargit.js holds the config variables in the js directory.
Content visible to verified customers only.
Maybe you set that to 0?
2. You can change your preview sizes all you wish in upload options but what is the supersize setting? You would need to rebuild the preview images in admin scan database but that requires your supersize to be larger than preview image. If supersize is 250 then you have nothing to rebuild from and they will stay at 250. If you say set supersize to 1024 and preview to 400 then upload a new ad to see it work. It all depends on your settings and if previews have been rebuilt.
3. Photopost has Lightbox not Enlargeit which is something similar already. These are totally separate products and Photopost does not come with enlargeit thus not really something you can add. All our products are supported as released.