On the whole Ab minor topic, can't you completely ignore the key signature to play the song in A minor (with the exception of making naturals into sharps)? I'm not entirely sure and would like to know, because I might end up doing this at some point.
There is a neat little trick you can do regarding that.
What you are doing is transposing the work up/down one semitone, or one half-step. In songs with few accidentals, it's easy; subtract the number of accidentals you currently have from seven. That number will equal the number of opposite accidentals the new key will have.
For example if the song has five flats, take five from seven to equal two. That's your number of sharps. Use the key of D major rather than Db major (or equivalent minor keys), and play as written.
If the song has any accidentals floating around (especially some minor keys), you'll have to mentally transpose the notes as you go in the proper direction.
Hope that helps a bit.