On #3 above I think you meant to put "created by a non-SOT on a Form 1".
As for #4, you do get the approved Form 5 back as your registration paperwork. No stamp is attached because you did not pay a tax. I know a widow lady who has approved Form 5's for her deceased husband's suppressors. If you want to sell it, you then do a Form 4 to the new owner.
Yes, meant Form 1. Finger-brain interface issue.