Image size for responsive pages

I’m trying to decide about image management in Wappler and how they will work on my responsive pages. When I used DWZone extensions it gave me several options for files including a thumb etc.

I would like to upload a few files as possible obviously but I don’t want to bog the pages sown when I load multiple images. My press guy likes 1000px files for press releases but that’s going to be too large for general page use correct?

Any recommendations on files size that works well with responsive page size breaks?