My shelf has been on hold for a while. It goes off of hold tonight. So, it's been a while since I have sent out books with D/C. I can use my own stamps with D/C and send it from my house or put them in a blue box, right? I know that I must include the 19 cents and that if it's over 13 oz. I have to bring it to the PO.

Yes.  It might not get scanned for awhile so if are using it for instant credit-it won't be so instant.  It may not even get scanned until it gets to it's destination.