I would not be concerned about the WAN IP address changing, and Verizon should insure that your connection is not vulnerable to denial of service type attacks. Your WAN IP address from Verizon is dynamic and the lease period is 24 hours or less, so it is not unusual to have it change.
You should just concentrate on using a good antivirus and antimalware program periodically along with using WPA2 security on your wireless with the WPS turned off in your router to keep your local network free of unauthorized users.