As the topic says.
Is it possible to upload a clipart library to Fancy Product Designer with for example 1000 categorized vector images that customer can choose from?
Yes. That feature is called Fancy Designs. Take a look at an example in this demo: http://fancyproductdesigner.com/product/t-shirt/
Yes, but can I upload a whole clipart library with for example 1000 images categories and names in one go, or do I manually have to upload them one at the time and manually name and categorize them? The link does not display if the library upload is possible.
You can use as many as the WordPress upload features can take in one go - not sure how many that is. Also depends on your file sizes I guess.