Is there a way to have a field created on a form based on completion of another field or use of a button

Here is an overview of one project I'm trying to accomplish. 



Blue circle = User field
Red circle = Text- Multiple Choice field
Black circle = Text- Multi-line field


In this form the project manager could need only 1 approval could need 6 or more. The sign off and comment fields are only editable by the user set in the respective approval field. The user is notified via email when they are assigned to an approval. There are other tables and forms within this app that need to remain view-able to users in the approval fields. 

Things I need to happen:
1. Project manager is notified via email when all assigned approvals are complete. Needs to be 1 email only not an email for each approval
2. Blank approvals(and corresponding fields) need to be hidden, but the approval fields still need to be editable by the project manager at all times