This scenario comes up from time to time. You'll need to create  an event
handler that changes the permissions  upon submission of the item. You might
need to do a little searchin to find what you're looking for. But you'll
have to write custom code to do it.

yes you will need a workflow  to do that. In that workflow you will have a custom
activity that add and remove permission  accordingly.

If you are using MOSS 2007, there is a cutom activity on Codeplex for
permissions.

For SharePoint 2010, the activity is available out of the box.

The problem part is that document creator always have read  rights on the
document, even if the read rights  are taken away. But you can use versioning and
draft item security to let the user  see the changes he made, and not the changes
made by any other user until documentis approved. Explore the Versioning
Settings of the document/ form  library. I am sure it is a zero custom code
project.

Although workflows can be used to do this it is an inefficient way to accomplish
the task. Workflows require a lot of overhead that isn’t needed when what
needs to happen can be completely automated. In this case an EventReciever is a
much better solution.
You can drive a nail with a wrench if you try, but that doesn’t make it the
right tool.