1) Is there any reason to save old wallet files if I'm generating a new backup after receiving some BTC?
2) Is there even any reason to generate a new backup after receiving some BTC or does the wallet backup just contain the private keys associated with the public keys, and it will be the exact same file regardless if the balance is updated?
3) As I understand it, an offline/paper wallet saves the private key to paper, and this is required to send money from that address. Is this right?

Thanks.