I think Microphone is a great choice for the starting song.
For that, you should pick something fairly new and really powerful, and Microphone obviously meets those requirements.
For the other three songs, I say pick one popular ballade (HEAVEN, Dearest, Days...), one experimental/non-traditional pop song (Duty, Bold & Delicious, Don't look back...), and then one of your favourite songs that's either a classic (M, A Song for xx, Boys & Girls...) or a song that you feel represents Ayumi well (what ever one of your favourite songs may be, that you would use to show off Ayu
). Try to not pick the three songs from the latest album, or all from the same eras or such, so that it's more interesting.
For the theme, you should go with what ever era the song that you choose to auto-start is from. So if you choose Microphone, definitely go for the Rock'n'Roll Circus theme. If you choose, say, Dearest, make sure you have the I am... theme to match that.
For images, definitely make sure you pick a wide variety of the styles she's shown us.
Just pick which ever pictures you love best, from the beginning, and the middle, and the current parts of her careers.
Good luck! ^_^