My Pipeline looks something like this:
lead -> qualify -> get qualified lead to upload 2 files -> transfer lead to consultant -> invoice -> win/close opportunity

My question is: 

How do I enable our leads to upload the requested files, and have those files be stored with the lead info in the CRM. The CRM would check the files are there, and approved by sales person (meaning the sales person verified the documents are ok), then once its approved by the sales person, it gets assigned to the consultant, and the consultant handles the account from there on out.