Long story short, I have an iPod 5, and I've been excited for this game for about a year now. I keep getting a GPS signal not found. Can I play under wifi or some sort of cellular data?
You can not play Pokemon GO on an iPod Touch 5G reliably.
As Pokemon GO requires players and their devices to provide the game with an accurate position (which WiFi triangulation does not), you will face frequent GPS errors.
In order to pull off positioning with WiFi reliably, you need to be in a very WiFi-heavy location (at least 10-11 networks with location data assigned). These, unfortunately, are not too common unless you live in a major metropolitan area.