(1) There is no configuration option which allows for the font size of the Gallery Title to be changed.
However, you can change the font size of the Gallery Title using CSS. Try adding the following code to the <head> section of your gallery's web page (changing the value for the 'font-size' as appropriate):
<style type="text/css">
.jb-flag-large-screen-mode .jb-area-large-mode-title {
font-size: 50px !important;
}
</style>
(2) When the image number is displayed, the caption will be centered in the remainder of the caption area (the part not taken up by the image number). The area required for the image number is always reserved to ensure that long captions that need to be wrapped do not overlap the image number.
If you want to push your caption along a bit, you can add non-breaking spaces ( ) to the the start of your caption text, for example:
<caption><![CDATA[ Caption text goes here.]]></caption>