Page number only starts at 2 or 0, for even-layout page

One way to achieve what you want is to dispense with the gutter and the mirror margins and set the Section to have Different Odd and Even Headers\Footers, and then insert a TextBox into the Header that extends down the right hand side of the page for the Odd Page Headers and a similar one that extends down the left had side of the page for the Even Page Headers and set the text wrapping for the text boxes to tight.  

If you make the width of the text box such that it displaces the text by the same amount as your gutter, it will have the same effect.

You do not then have to modify the page numbering and if your document has a Table of Contents, it will reflect the correct page number, which will not be the case if you use a "calculated" page number.

Here's a sample document that illustrates how to modify the page number field: Even page with odd page number Follow these steps, or just copy and paste the page number field from the sample:

1. In Word, open the page 1 header/footer so you can view the current page number.
2. Delete the page number field.
3. With the cursor still in the same spot, hold down Ctrl and press F9. This creates a blank field: {  }.
4. Click in between the 2 curly braces and type =
5. Now hold down Ctrl and press F9. The field now looks like this: { ={  } }
6. Click inside the innnermost curly braces and type PAGE
7. Click in between the second-from-right and the rightmost braces and type -1. Your field should now look like this: { ={PAGE}-1}
8. Select the whole field, right-click and choose Toggle Field Codes. If necessary, right-click on the filed and choose Update Field. The number should change from 2 to 1 because of the math function we included in the field. The equals sign alerted Word that this is a formula and the minus 1 subtracts 1 from whatever result Word calculates.