There should be no second guessing here.
You did the right thing by ordering the chips and optics.
There is no way around the SET chip for enabling your bill validator and if your paying for shipping for one you might as well get both.
If you don't need it today then you will need it sometime in the future.
I am not sure how much reading you have done on this forum but if you turn out the lights you will soon see that these machines multiply and having the right tools to maintain the fleet is a good idea.
…. and if you google "fleet" you will find that it means more than two..... just saying.....