A family of Microsoft word processing software products for creating web, email, and print documents.
Different first page is a property of the Header, itself, whereas Headers/Footers & Layout specifications (margins, orientation, paper size, columns, etc.) are properties of Sections. If you want to vary the Layout you need to create appropriate Section Breaks, then change the specifications for the respective Sections.
MVP Suzanne Barnhill provides an excellent tutorial for creating a multi-page letterhead template. It uses the Windows version as a model so you'll have to do a little 'translation', but if you intend to do this with any degree of frequency [i.e., more than once] it's well worth learning what is required to do it right: