(1) After creating an album, open the 'index.html' file (in the album's root directory) in a plain text editor, scroll down to the CSS section of the page and just after:

body {

... enter the following (the default value for Juicebox-Pro's galleryFontFace configuration option):

font-family: Helvetica Neue, Helvetica, Arial, sans-serif;

(2) The minimum requirements for Juicebox-Pro's email functionality are that you set showEmailButton="TRUE" and use a valid email address for emailAddress (in the skin's 'Pro Options' text area). With this is place, the Email Button will display on the gallery's Button Bar.
Please note that you'll need to ensure that you are using Juicebox-Pro for this to work. (Email functionality is not supported by Juicebox-Lite.)
Instructions for upgrading the skin from Juicebox-Lite to Juicebox-Pro can be found in the skin's description on its download page here: https://jalbum.net/en/skins/skin/Juicebox

(3) Thumbnails do not have to be square but they do all need to be the same size as each other.
You can set the thumbnail dimensions on jAlbum's 'Images -> General' tab (in the 'Image bounds' control panel) and you can then tell Juicebox the thumbnail dimensions by setting thumbWidth and thumbHeight in the skin's 'Pro Options' text area, e.g.:

thumbWidth="100"
thumbHeight="60"

Please note that, just like #2 above, you'll need Juicebox-Pro for this to work.

I hope this helps.

(1) Juicebox-Pro has only one text color setting (textColor) which is used for all gallery text.
However, you could set a textColor for your gallery and then override the color for your Gallery Title by using CSS (in the album's 'index.html' page), e.g.:

/* GALLERY TITLE - LARGE SCREEN MODE & SMALL SCREEN MODE */
.jb-area-large-mode-title, .jb-idx-ssm-title-wrapper {
    color: #ff0000 !important;
}

textColor can be found in JuiceboxBuilder-Pro's 'Customize -> Lite' section (and should be entered in the Juicebox skin's 'Pro Options' text area).

For reference, a full list of all Juicebox-Pro configuration options can be found here.

(2) The position of the image's caption text is determined by the Pro configuration option captionPosition.
Possible values for captionPosition are OVERLAY, OVERLAY_IMAGE, BELOW_IMAGE, BOTTOM, BELOW_THUMBS and NONE. A short description of each of these values can be found in the Caption Options section of the Config Options page.
The only way to have the caption text displayed to the left or right of the image would be to set thumbsPosition to either LEFT or RIGHT and then set captionPosition to BELOW_THUMBS, like in this demo here.