Question, is there a way to export my Lightroom pictures to your album? (Or is that more a function of JAlbum.)
Until you click Make Album, the skin isn't really involved. The jAlbum core is responsible for keeping track of the images in the project. I'm not an LR user, but I believe you can either just export your chosen images from LR, then feed them into the project, or you can set up your project, define the directory in which the source images will be found, then set up a LR publish service to disk, specifying that directory.
Is there a way to display comments and IPTC data? For instance when I mouse over the picture.
Comments are normally displayed under the slide image. Tell jAlbum where to get the comments - see Comment sources on this panel: http://jalbum.net/help/en/jAlbum/Settings/Advanced#Metadata. Then you can tell Projector what to display below the image - see Projector > Lightbox > Caption/Buttons > Caption template.
For other metadata, like IPTC or xmp fields, see Projector > Lightbox > Photo data. You can choose any metadata fields that are present in the image. To see what metadata fields jAlbum can detect, right-click a thumbnail in the jAlbum Explore view and choose List metadata. Under the slide image, a little "camera" icon will appear - when hovered, it will display the chosen metadata.
I simply "export" the images in a subfolder along the originals and drag and drop them onto jAlbum. I'm not sure Lightroom can export deep folder structures at once, but if that's possible you can drag and drop the top level folder onto jAlbum and it will keep the folder structure.