without knowing what kind of services you want to use, I can only say with what kind of services I do it:

I am using a clientside upload using s3 pre signed upload urls. With that I generate a url for each file and upload each file with the specific restrictions, that I set serverside. The upload form should be easy: a form with an input of type file and with "multiple" prop

@Cairn Terrier what else do you need?