I bought Juicebox then if i wants to buy it, i don't need the Showkase Pro Version, then installing Showkase Standard and Juicebox, my version will be a Showkase Pro version ?
Essentially, yes, although the Showkase Pro Viewer Bundle includes both Juicebox-Pro and SimpleViewer-Pro.
However, if you intend to use only Juicebox-Pro in your Showkase installation, then Showkase Standard would be fine for you as the only difference between Showkase Standard and the Showkase Pro Viewer Bundle are the Pro viewers themselves.
About filenames, do you keep the names entered for the differents folders, images and thumbnails and are you finally full SEO ?
If a page is named 'This is a page', then the corresponding folder will be named 'this-is-a-page'.
Images uploaded to the 'Image Library' retain their original file names.
If using Juicebox and SimpleViewer galleries within Showkase, then any SEO issues which would apply to the galleries themselves will still apply (although Google should be able to index data stored in XML files).
It is possible to create subgalleries and sub-subgalleries for example :
It is possible to create a top-level 'Gallery Index Page' which features multiple galleries.
However, it is not possible to add a further 'Gallery Index Page' to an existing 'Gallery Index Page'.