The custom CSS is asking for h6, but the code delivers h5
h6 is used for displaing tags/category.
Also, the custom CSS is showing before the css file, so I have to use !important for some css, and I don't want to
Your theme have a little bug. Function wp_header must by the last before </head> tag. In Your theme is before theme style.css. Check it please.
Having a way to add a custom title, if we don't display the header
You can use iworks_upprev_box_before action to put anything what You want to put.
Having the possibility to customize the div template. At least, possibility to have the h5 before the image, so the title could be the box width long
At last You can use iworks_upprev_box_item filter to change anything in each upPrev item.