I work with saddle stitched booklets all the time. The real answer is what does the printer want from you, and what are his capabilities.
When I am asked to print a booklet, I have them output into a pdf from page 1 through page N. This way, we aren’t confused with the difference between reader spreads and printer spreads. Almost any printer, especially one printing on a digital machine, has the ability to “impose” the pages as the last step in their process, so giving them pages 1-n is perfectly fine.
If they insist on you imposing the document into a printer’s spread (with page n&1 on one side, 2&n-1 on the back side, also known as page 2 of your printer’s spread, and so on until you have page n/2&n/2+1 as the last spread), you can either lay it out like that or use the export booklet feature (or some post-processing imposition solution – I like Rhimposition script for InDesign). In your case of 4 pages, that is simply 4&1 and 2&3.
Since you have perhaps the most trivial case of a booklet (4 pages), just ask if they want pages 1-4 of letter size, or if they want printer spreads of 11×17. You could lay it out easily enough, or use the export booklet feature to do it.
An aside, and for completeness, the tricky stuff comes when they have images and graphics that bleed across the binding edge. Laying them out on 11×17 spreads in what is called reader’s spread (they way you would see the inside of the finished piece) is best. This is the default for InDesign when it uses “facing pages” on a new document. It is much easier to work on a document this way when you have these designs. Then you make the decision to send the printer the individual pages or export them to a booklet (which simply converts it to a printer’s spread).
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