Workflow with multiple approvers

I need to setup a document workflow, where the uploader can specify upto 10 approvers, and the document should be published only when all approvers have approved the document. My questions:

  1. how to provide for the uploader to specify multiple approvers? Use people picker with multiple users?
  2. How to setup the workflow?
  3. Usually the users from the approvers group can approve the document. Here since the uploader can specify any user to approve, will we need to have the workflow set “approve” permission for each user specified?
  4. I tried using the built in Approval - sharepoint 2010 workflow. I wanted to set this workflow to be manually executed, so that the second form comes up where the uploader can specify the approver names. However the option to set it to manually execute is greyed out (I have enabled versioning on this document library). what could be the reason?

I am using SharePoint 2013 on-premise Standard edition