Edit > Select all will allow you to add everything to upload at once.

If you are going to be uploading large batches at a time, I would suggest only having those in your My Items at uploading time. That way you can select all to add to upload, then delete them from your My items.

You can set up sub-folders under All items or My items, so maybe work out how many different upload sets you will be working on then put the items for a particular upload event in a folder for that upload.

ie If you want to upload 100 items every Monday, then set up 4 folders - Monday1,2,3,4 and do the listings for the items for the relevant Monday in the relevant folder. Once a particular set of listings has been uploaded, empty the folder and it is ready for reuse with no confusion as to what's what.