Q: if i only use the internet and only download while connected to wifi, will my data allowance be uneffected? thanks

The safer way to not use your allowance is to turn off Settings > General > Cellular Data as detailed here:

iOS: About the Cellular Data setting

If cellular data is not turned off some functions will use small amounts even if you are connected to WiFi. And remember that WiFi is turned off to save the battery when the phone goes to sleep unless it's plugged in, so any background data use will then go over cellular.