For a beginner who doesn't yet have his ear developed to the point where he can learn tunes by playing along with recordings, it would be helpful to either learn ABC notation or staff notation, or both.

ABC notation is favoured by traditional Irish musicians, many of whom feel that ABC is superior to staff notation. The great thing about ABC is the vast corpus of tens of thousands of Irish tunes available in it, on sites such as thesession.org. And, you can simply type ABC notation on an ordinary keyboard.

I myself have always been able to read ordinary staff notation and I feel that it's the best. I have a hard time reading ABC. But the majority of traditional Irish players disagree!

About whistle keys, if you do enough playing you'll end up requiring whistles in every key. Here's what I take to a gig:



It has in it every chromatic key from Low D to high Eb. Mostly Burkes for the low keys and modified Generations for the high keys. But an MK low D, a Feadog high D, Susatos for the odd keys of F#/Gb and G#/Ab, and a Bernard Overton Low E.