> Does this sound about right at this early stage?

Pretty much. To edit and sweeten the sound, use a PC recorder
like Goldwave www.goldwave.com which, although slightly
crippled, is essentially free for what you need. ie record clips
with a better microphone, enhance the messages' tone to best
suit the ISD bandwidth (eg bandpass or EQ) and edit clips for
length, remove unwanted noise, etc. Then program the clips via
Line Out into ANA IN. Clip start addresses then go into a PIC
table for look-up

The above would be fairly easy for a one-off. Otherwise Harold's
Quadravox for a more production-line approach

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