The shortcode specifies how the initial gallery display will look like.
Lightbox is an overlay, based upon the current initial display, and activated by a click on an image. So, lightbox is not an initial display type and can therefor not be specified by a shortcode.
In Table VI you can specify what kind(s) of initial displays should produce a lightbox overlay when you click on a type of image.
This is the way it is designed and how it works.
The indication of the maximum upload capabilities is an estimation based on server parameters that are available to the programmer. Unfortunately there is no standard in what parameters that are used here are granted to be available. In most cases this calculation is correct, however as it says: Additionally your hosting provider may have set other limitations on uploading files. not always. You can turn this check off in Table VII-B3.1 and 3.2
When you open the Import Photos admin page, You will see that you can import photos from your so-called Depot directory. It will say that the depot is empty. You can see the path where your depot is.
You can ftp photos to that directory and import them to wppa+ using the Import Photos admin screen. You can switch to a different directory ( see Import photos from: ) and set it by pressing the Set source directory button.
You may also ftp zipfiles to the depot. They are importable in two passes, the first will unzip the file(s), the second pass you can check which photos to import to what album.
The out of memory error you got was during the creation of the thumbnail image and is related to the size of the original image in pixels. Try resizing your source images on your local pc to the desired final pixelsize