Someone please answer question about data usage

I have a "Remote" app on my iPhone that allows me to home share with my iTunes library on my iMac at home to stream music. Does this use data on my phone, or does it work like bluetooth and just use the battery? Regarding Pandora, if I understand correctly, this would use up my data plan since Pandora streams across the Internet, right? If I am right above, is the basic rule of thumb that anything where the Internet is needed would use data whereas anything just using your home network would not, right? If I am at home, and I have both wifi and cellular active on my iPhone, which of the two will my iPhone use on the Internet? Again, in this example, if I am streaming music on my phone using the remote app, will my phone use wifi or cellular?