Dear friends, for a single-player layout consisting of just two pages, I would like to change the page numbers so that they are positioned on the outer margin. At the moment, they are on the inner margin. Is there a simple method for that setting? Thanks!
Ludger,
They are not on the inner margin.
What you see is page one front and page 2 of the back of one sheet of paper.
In layout options you can change the first page to start with page no. 2
Then you will have page 2 (not visible) on the left and page three on the right (with page numbers at the outside margin).
It is important to know that there is a standard: odd page numbers (1,3,5…) are on the front and even numbers (2,4,6…) on the back of a page (=if you turn over).
(Rather than front and back, I would say that it’s usual for odd page numbers to be on the right of a spread, and even page numbers on the left.)
Yes, and spreads are quite common when it comes to instrumental layouts for smaller pieces.
You probably don’t need the Flow heading for a 1-flow piece. 
In publishing, a spread is any two left-right pages, not just a single pair as you have in a short piece. In a longer layout, 2-3, 4-5, 6-7 etc. are all called spreads.
Page orientation is also called recto and verso—which literally does mean front and back. The reason I find it a little more useful to talk about left and right instead of these other terms is that in a single 2-page spread, as the OP has, it’s not immediately clear why the left page would be the verso/back of anything—both pages look like fronts to me.