Will rib cartilage harvest affect my ribs as far as strength of the ribs?

Overall, it depends on how much cartilage is needed and where they take it from. Generally speaking, it is usually a small amount taken from the lower ribs, and should not cause issues later. For the most part, it should also repair itself over time. Although I would advise not getting tackled right after the procedure, it should not cause weakness after the fact ( depending on what sports you play, you should take a little time off as it will be uncomfortable to move around a lot).