First, see my response to your earlier question.

Ribbon versions of Word have special building blocks called cover pages. You may want to start from one of those.

You can restrict editing using the button on either the Review Tab or the optional Developer Tab. You can make exceptions to allow editing everywhere except your cover page. In addition, you can use Content Controls in your cover page and allow typing in those but not allow them to be deleted or moved. You can restrict how much text is put in those Content Controls. You can use StyleRef Fields or linked Content Controls to repeat information typed into the Cover Page elsewhere in your document, such as in headers or footers.
Word Content Controls

Styles can override or ignore margins. You can use styles that have left and/or right indents that are inside or outside of margins for text on your cover page. Likewise, graphics like shapes and textboxes can ignore page margins. You do not need different margins there.

I would again urge you to do the reading suggested in my other response. These features all tie in with one another.