re: % of Credit limit to use each month?

This is correct in principle, although I do not know the exact percent at which it becomes a problem. I put pretty much everything on my rewards credit card, but I also pay it off in full each month.

However, the credit report does not show the zero balance carred over. It shows the amount spent as of the monthly statement (before I get a chance to pay off). It has been noted as a deficiency on prior credit score reports. Since the credit score is still high, I have not put much thought into it.