Questions 1 & 3 : I only use .ZIP or .RAR to wrap files for sending via email, never for my data backups which I save without using any utility software.
Reason? --- .ZIP & .RAR or other proprietary backup archives can become damaged/corrupted so you risk losing everything that's inside it.
Question 2 : Check settings and options in your antivirus software to see if "delete" can be changed to "quarintine" when a suspected virus is found.
Question 4 : Always keep at least two backups on two physically separate drives (I keep four backups on four external hard drives).