The same question appeared on a German forum a couple of weeks ago, and the consensus was that it was a bad idea, when starting to work with carbon, to start with a saddle/seatpost combo.
I'm not your mother and won't tell you what to do or not to do, but personally I'd start with easier, smaller and less critical parts, and I'd definetly not rely on it being cheap. Apparantly it's an expensive and time consuming hobby to make cf parts. I looked into it once and shyed away after foolishly following someones advice and googled vacuum pump.
Maybe you should start a "how to work with cf" thread in the diy section where more experienced people could suggest parts that are fairly easy to make, don't need a lot of material and won't hurt you if they break.
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