This option is available to Juicebox-Pro, too.
Juicebox-Lite accepts only the Lite Options and the Embed Options on the Juicebox Configuration Options page.
Juicebox-Pro accepts all options on the page.
Just make sure that you have set showExpandButton="true" in your gallery's 'config.xml' file.
Please note that the 'Expand Button' will be displayed only if the gallery is embedded in a page at dimensions of less than 100% of the browser window size. Otherwise, the gallery will already be displayed as large as possible (100% x 100%) and the 'Expand Button' would be redundant.

That is correct.

It would be more accurate to say that the caption and title sit over main image area.
You could ensure that the caption sits at the bottom of your main image (though it would still start beyond the left of the main image) by increasing the size of your main images to dimensions beyond most monitor resolutions. Juicebox would then dynamically scale your images down to fit the main image area and there would be no space at the bottom of the main image area (below the main image) where the caption is positioned.

@Rainer

Thank you for the suggestions.

Juicebox features many Configuration Options which can be set by the user very easily.
To modify the layout beyond what is capable with the preconfigured options, please see the Juicebox Theming page. This involves modification of the gallery theme's CSS and/or image files.

I think it is unlikely that anyone will write a Juicebox plugin for Lightroom with a user interface which features all possible configuration options.
The user interfaces for most plugins (I'm thinking of AutoViewer, PostcardViewer, SimpleViewer and TiltViewer here) feature only Lite options. In order to incorporate Pro Options in a plugin-generated gallery, the user could either manually edit the gallery's 'config.xml' file or open and edit the gallery in JuiceboxBuilder-Pro (which does have all Pro Options available through its user interface).

JuiceboxBuilder-Pro creates a complete gallery folder. The 'index.html' page within the gallery folder can be used to view the gallery on its own page.
JuiceboxBuilder-Pro also supplies the user with embedding code (on the 'Publish' tab) which can be used to embed the gallery in an existing HTML page alongside other content (following these instructions).

This is by design. The 'Toggle Info' button toggles the visibility of all elements in the OVERLAY (as defined in the Button Bar Options section of the Juicebox Configuration Options page.
You could either set the position of your Back Button to 'TOP' or overlay it on top of the gallery (but not as part of the gallery) as you have done with your SimpleViewer galleries.
As this is not technically a bug, it might be wise to post your suggestion in the 'Feature Requests' thread so that it is not overlooked. Thanks.

I see these two issues, too (Win 7 SP1 x64).
I do not know if they can be fixed but I will log a bug report nonetheless.
Thank you for reporting.

This is due to the default setting of enableKeyboardControls="TRUE".
If you click on the browser's address bar (to take focus away from the gallery), the F5 key becomes active again.
If you set enableKeyboardControls="FALSE", then the F5 key is active, even when the user has been clicking in the gallery area.
I will try to find out whether the F5 key can remain active for both values of enableKeyboardControls in a future version.

This is by design. Small Screen Mode does not support color options.

You have two instances of Juicebox on your page:

        new juicebox({
            containerid : 'juicebox-container'
        });

... starting at line 49 and:

new juicebox({
containerId : "juicebox-container",
backgroundColor: "#FFFFFF"
});

... starting at line 93.
Both instances are being embedded into the same <div> and the first one is momentarily displayed before the second one replaces it. Because the first one has no backgroundColor explicitly specified, it will use the default color of '#222222' which is what you are seeing as flashing.
Use only one instance and delete the other. If you choose to use the first instance, add the backgroundColor : '#ffffff' parameter to it and leave the following code on your page where the second instance currently is:

<div id="juicebox-content">
    <div id="juicebox-container"></div>
</div>