If you haven’t already, I’d recommend taking a look at our Interactive Tutorial, available from the Help menu. It’s a good overview of Scrivener’s fundamental operations, and your post reflects some confusion in that area.
If you select multiple scenes in the Binder, the footer at the bottom of the Editor pane will show you the word count for that selection. There’s no need to do any math. (View -> Editor Layout -> Show Footer will show this bar if it’s been hidden, View -> Scrivenings will show the text from all selected documents at once.)
You can also show the word count for multiple scenes in the Outline view. View -> Outliner Options lets you choose which columns to show.
RTF format absolutely supports headers and footers. I use them myself all the time. Edit your Compile format and look at the Page Settings tab. See Section 24.20 in the Scrivener manual for more information. Similarly, stripping out identifying information via the Compile command is trivially easy.
Katherine