CSV importing/exporting is quite good with the new ModelAdmin, that seems to make good use of a CSV import / output tool. I'm not sure Ecommerce has this support yet. I know that one of the core devs did product CSV import for https://sunshinepharmacy.co.nz/, don't know if this work has been released yet but the backbones for it are there at least.
Bulk uploading files - in the CMS you have to select files from your computer one by one but you can upload those in a group. Other way to bulk upload is to just do it via FTP. Your FTP software should support dragging folders and multiple files etc, and thats probably the quickest method for bulk files