You could leave all the fields on there and not make them required, but put a Wait Condition into your workflow that doesn't allow the document to progress until the appropriate fields have been filled out. Also, put it into a Business Process step so that they'll see instructions for what fields need to be filled out. If they save and close the document without making the appropriate changes, you could route it back to them with a *Required fields: Name, value, Date* label inserted into the file name and/or send them an email.

Another, more invasive option, would be to have a minimal starting template that doesn't have all of the necessary fields. At each step of the workflow individually add the fields that you need the next person to fill out. I'd still use a Business Process in order to get some instructions in front of them and add some traceability. Also, the Wait Condition would make sure they couldn't get away without filling in the necessary fields. Each person would only need to worry about the blank fields that have been added specifically for their work. Then at the end of the workflow take your minimal template and additional fields and transfer the data into your full final template.