The amount of artworks you can upload will vary according to which plan you have chosen. In the Basic plan you have up to 80 artworks, in the Advanced you have up to 500 artworks and in the Premium one you have up to 2000 artworks.
The artworks limit is lifetime, this means you can upload up to the given amount of artworks on your plan. However, you can always delete some artworks and replace them for new ones.
Please visit https://www.artplacer.com/pricing/ to see all plans and features.