Pledges are per visualization. Currently, I create a couple of visualizations per year, so if you pledge a dollar you will not risk going bankrupt.
The source code for my visualization will be open sourced and put on GitHub. So if you want to change visualizations and host them for your own needs, that will be fine (for instance, you might wan't to integrate them into to your own course material and add more explanations).
The actual visualizations are licensed under a CC-BY license, meaning that you are free to, for instance, take a screenshot of them and include a static image in your research articles or presentations.
Some of examples of my work can be found here: