Question.  I am confused by rule d. Does that mean we can only glue no more than 4 together and that no part of our machine can be more than 4 spaghetti wide/thick?

Answer. Yes for the first part of your question: not more than 4 strands together otherwise teams can glue strands together resulting in basically a glue structure rather than a well-designed structure.  However, the device can be designed with parts thicker (wider) than 4 strands of spaghetti.

Remember that it must be clear to the judge(s) than the sole purpose of the glue is to attach spaghetti strands together.