Does the unlimited texting/calls add-on include pictures and videos or does that go against data?
Those go against data so wouldn’t be included in the add-on.
Does anyone know if I’m Texting a video or picture over wifi, will I get dinged data?
If you send it as an mms, i.e. through your texting application, then yes it will count. But if you have an iPhone and you are sending it as an iMessage, then it won't.
If you are sending it as a whastapp message or using other IM apps. They won't count towards your data bucket if you're connected to wifi.