You can find some answers and further links in this thread: Speech module - change to a male voice?
1-2.
Yes you can customize the voice, but there’s no easy way of finding out which other voices are available. Better support/API:s are coming in SDK33 (see link above).
3-4.
I’m not familiar with how these services work, but if they’re able to talk to your app over some kind of HTTP API then it’s probably possible to integrate it.