I heard its not good to wax your vagina all the time. You need hair there to fight off bacteria? Is that true? If so, what is a good amount to wax off

Not sure of that. I've never heard that. In fact, it's more hygienic to wax. Hair will attract and keep bacteria close to the skin rather than let it wash off. You do have to be careful with skin irritation though because that can lead to a skin infection. Keep the area medicated with a solution recommended at your waxing salon and keep the area moisturizer if necessary.
Vulvar Hair. I am not sure I am aware of any facts saying the vulvar hair is protective. In fact, crabs can attach to the hair and cause problems. I think if you have hair, it is important to keep it clean. I you wax, you can get infections that can be serious. I have heard that hard wax is better than the sticky soft wax. Hope this helps.