1)  Yes.

2)  Yes, you put "7" on the DCN line.  There is no need for an "X", except to mark the "Depreciation or Amorization" box just above the DCN area.

3)  This link will probably help:  https://portal.clientwhys.com/sites/11009sang/form-3115-line-by-line-current-kj-to-pdf-to-ppt-111017...

Yes, you can attach a PDF to the e-file, and mail the second copy to the address in the Instructions.