Backwards answer:
the flashing led works - I don't know why yours doesn't
but check settings -> notification light ?
I have mine set to light up for email and I never ever use Modest
but the light always shows up when claws get an email.

addresses - I never use an address book (too lazy I guess)
but you can harvest addresses under tools>collect email addresses

you should also be able to import emails from Modest,
haven't done it but the emails are in /home/user/.modest/
but no promises there...