… how do I fade the audio in and out at the beginning and end of the clip? I cannot get the small pick-up points to appear once I introduce a transition?…
No, that it is - in iMovie - automatically done.
a cross-dissolve dissolves video AND audio.
If you want for any reason a audio-fade-in/-out BEFORE the video-dissolve, you have to extract the audio, apply your personal fades, and apply a video-dissolve then...
... for my personal taste, that looks/'hears' odd.