It all depends on how much you plan on smoking. If you're gonna have the pipe in your mouth all day, well, yes, a rotation is required. Although some do smoke the same pipe all day, they just clean it once each bowl is finished.
If you're gonna be a sporadic smoker, one pipe is alright. A second or third one as backup is OK, but not an absolute necessity. I smoke ~1-3 bowls per week and have 17 pipes, one of which has never been smoked, and a few which are smoked very seldom.
As Casual said, cleaning is key. Treat your pipe as a firearm: clean it thoroughly after each firing session. Removing the 'fouling' does wonders to avoid tars building (which leads to souring), and to prevent ghosting. A clean pipe is a happy pipe.
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