This is possible only with Juicebox-Pro (but not Juicebox-Lite, the free version).

With Juicebox-Pro you can set the thumbsPosition (the position of the thumbnails: TOP, BOTTOM, LEFT or RIGHT) and maxThumbRows and maxThumbColumns.

When thumbsPosition is set to either LEFT or RIGHT, the number of thumbnail columns is fixed at the maxThumbColumns value whereas the number of thumbnail rows is variable (up to the maxThumbRows value) depending on the dimensions of the thumbnails and the space available in the user's browser.
Take a look at this demo gallery with 3 columns of thumbnails: https://www.juicebox.net/demos/pro/simp … umbRows=10

When thumbsPosition is set to either TOP or BOTTOM, the number of thumbnail rows is fixed at the maxThumbRows value whereas the number of thumbnail columns is variable (up to the maxThumbColumns value) depending on the dimensions of the thumbnails and the space available in the user's browser.
Take a look at this demo gallery with 3 rows of thumbnails: https://www.juicebox.net/demos/pro/simp … ion=CENTER

With Juicebox-Pro, you can create a Multi-Size Image gallery.
The Medium images will be displayed in the gallery and the Large images will be displayed when the images are opened on pages of their own.
If you do not want a Multi-Size Image gallery, then you can assign a unique linkURL for each image (which you could point towards a large image).

Set imageClickMode="OPEN_URL" (in JuiceboxBuilder-Pro's 'Customize -> Main Image' section).
If the image has a linkURL associated with it, then, when the main image is clicked, the linkURL will be opened in the linkTarget window (_blank, _self, _parent or _top). Otherwise, the largeImageURL will be opened and, failing that, the imageURL (the actual image used in the gallery) will be opened.

In Juicebox-Lite, you can use the Open Image button. (In Juicebox-Lite, it is not possible to change the image click functionality.)
Set showOpenButton="TRUE" (on JuiceboxBuilder-Lite's 'Customize' tab) to display the Open Image button on the gallery's Button Bar.
You can set a linkURL and linkTarget (click an image's thumbnail on the 'Images' tab to reveal the input fields at the bottom of the window) for each image.
You'll need to provide the large images yourself and ensure that your linkURL entries point towards them (with either absolute or relative paths).

I hope this helps to clarify things.
Please let me know if you have any further queries.

Yes. Just set showPagingText="TRUE" (in JuiceboxBuilder-Pro's 'Customize -> Thumbnail' section).
Here's a sample gallery using this setting.

You would need to set the linkURL entries for your images (on JuiceboxBuilder's 'Images' tab) and provide (and upload to your web server) the images that your linkURL entries point towards.

A linkURL can be an absolute path (in the form http://www.example.com/images/image_0001.jpg) or a relative path (relative to the web page containing the gallery's embedding code).

Juicebox will automatically use the linkURL entries in the following scenarios:
(1) showOpenImageButton="TRUE" and the Open Image button is clicked (Lite and Pro).
(2) imageClickMode="TRUE" and the main image is clicked (Pro only).
(3) showDownloadButton="TRUE" and the Download Button is clicked (Pro Only).

Don't worry about it. You are currently using Juicebox-Lite so your query is just fine here!