One more thing to consider…
When you create a new document without facing pages, you get a non-facing master page (also called a single master). Here's what it looks like in the pages pallet:
One thing you might like to have in a facing-page document is a facing master, but just changing from a single-page document to a facing-page document won't change the master, but you can do that afterward if you like. Go to the fly-out triangle of the pages pallet and select Master Options for "NAME OF MASTER PAGE HERE"…, as you can see here:
You will get this window:
Change the Number of Pages to 2, and your master page will look like this:
