Contrary to what you think, your entire document will be using facing pages!
… an 8.5×11 saddle stapled instruction book ..
— that means that whatever you do, the document will be printed as having “facing pages”, even if you set it up to have single pages in your ID document itself. Compare, for example, if you add a three-page spread somewhere inside your document. No matter what you do, without special instructions to the printer each page will end up on a separate page and you'll end up with three separate pages in your stapled document.
That is, unless … you output create your final PDF with the option “Print as Spreads” on. But you should definitely not be doing that if you're going to send the PDF to a professional printer!
So you can create your document any way convenient to you.
But if your final output is to be printed “as usual”, that is, not loose-leafed, I strongly suggest you use facing pages throughout, so you get a good sense of what the final product is going to look like. For loose-leafed, single pages make more sense (because that is, in fact, “how it's going to like like”) but you cannot insert a double-page spread in a loose-leafed document because it won't be printing that way. Not even if you create the document that way — the information of which pages are side by side to which others is only visible inside ID, and not exported into single-page PDFs. (Unless you export with “Spreads” — but I assure you your printer won't like that a bit!)
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