Current interface is booring, but actually very customizable, that's good, but at some time you could get lost around. My mind tries to rework this in a step-by-step one.
What if all those options will be in a something like vertical accordeon, and you can step-by-step move through slides choosing that you need being concentrated on that you really want.
One thing that really is missing is a color picker, also there was an idea that at first step of customizing you could start with a template or with a color scheme/palette.
Another good thing to add to the colors section is that when user chooses a color for background to calculate based on some funky relations the colors for headings, text, links and so on. To provide at each step tips about lack of contrast or for number of colors he chooses, you know what I'm talking about, you are in UI/UX field.
looks like a good sketch must be there.