Hello egravel -
to answer your last question first, Custom Item Specifics are available on the Auctiva lister once you have selected a category that makes use of them. Currently this option is available for appropriate categories just beneath the Item Condition Note field. The link will open a popup to add the Custom Item Specifics.
As for the issue with your images, it sounds like you may have added your images after you selected your template so the template selector was unable to acknowledge them. If you select your images prior to adding a template to your listings, the template selector will set to the number of images you have in your listing - otherwise, when you add your template you need to adjust the pull down for Images to the appropriate number.
If you are using an item details profile that has the template preselected, you can define the number of images on the template selector and then save the profile so the selector already has an appropriate number of images in it. If the number of images you use in listings varies, you can always set the Images pull down to 24 when assigning a template to your profile (note that have additional images selected in the template selector will not affect your listing if you use a lesser number of images than the selector is set for, but if you add the template first, it does not find any images and is set to 0, so when you add the images later none show in the template).