Google music on an iPad?

I'm looking to get my first iOS device, and have decided on a used iPad 3 or an iPad mini. Just a note, I would prefer the bigger iPad since this is basically for home use. My gadget situation right now: I have a Galaxy Nexus that I love, and a Galaxy Tab 10.1 I also love and use every day, but it's long in the tooth, and I'd like to try Apple. I have a Windows 7 desktop and a Windows 8 laptop (ugh). Any help you could give me would be appreciated.

I've looked at some of the Google Music apps on the appstore and a lot of them are rated rather low. Is there a reliable way to get Google Music on an iPad? I simply don't want to use iTunes if I can avoid it. ( Can I manage the ipad without iTunes?)

If I were to get the iPad 3 with Retina display is 16GB enough? From what I understand the Retina apps are huge. I'm buying this device because I want to go app crazy. I will not be loading movies or music on it (provided I can run Google music on it). Thank you for reading!