I've never come across a GMAT problem that was wrong because it joined too many clauses. That said, it's really hard to join too many clauses and still have it be grammatically correct. At some point, it would likely become a run-on sentence.
I'd encourage you to focus more on whether the clauses in the sentence are grammatically correct rather than the number of clauses that are joined.
Brett Beach-Kimball | Manhattan GMAT Instructor
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