Is it bad to teach high school science for a few years before attending graduate school?
Teaching experience is a good thing.  If you want to teach again after completing your PhD, the teaching experience will help you get a job.

However, I have doubts about your financial strategy.  In most STEM fields, you can expect to get paid more if you have a PhD.  The sooner you complete your PhD, the sooner you get the extra pay, and the more years you will keep the extra pay for.  I am not knowledgeable about teacher pay, but I suspect that the best American PhD programs pay students only slightly less than typical entry level high school teaching jobs in America.