Floating next/prev buttons

You might try experimenting with that sort of thing in a child theme, so your tweaks won’t be overwritten when updating the theme. Here are some guides in case you haven’t made one before:

http://codex.ww.wp.xz.cn/Child_Themes
http://op111.net/53/
http://vimeo.com/39023468

I took a look at the example site and then did a bit of Googling, I found this tutorial you might want to peek at:

http://www.jqueryscript.net/slider/jQuery-Plugin-For-Long-Content-Pagination-Slider-Plugin-Text-Pager.html

Or if you aren’t comfortable “rolling your own” you could explore some of these pagination plugins to see if one would meet your needs:

https://ww.wp.xz.cn/plugins/search.php?q=pagination+Slider