If I buy everything needed with a CC, and pay it all off before interest charges post, do I help my credit rating?

Interest charges are usually posted daily. Pay it all off before the statement closing date. On that date, your credit utilization ratio is reported to the credit agencies (usually). When, on that date, your ratio is calculated to be 0%, that's excellent.

Yes

Yes

That would have the same effect as not using the card at all, since in theory, a $0 balance would be reported each month.

If you pay it off in full, each month before the due date, yes.

yes