In reply to Oldsign:
"it's great to get a grounding in music as you will need to learn more theory than with guitar for example"
I definitely don't agree with this. To be a half decent guitarist you need to know every chord of each key in an instant, understand how these chords work together in progressions, the major, minor and blues scales at least, which of these scales can be played over which chords and understanding how each different interval sounds. To be better than half decent you need to extend that to modes, inversions, etc...
Of course learning harmonica or any other instrument properly is also difficult, but there's a lot more to playing guitar than learning wonderwall from guitar tab
Post edited at 22:21