[ecesena]

If you'd like to start simple, you could skip the voice interface and go for a text-based interface like Messenger.

Voice can be a layer that you put on top later, with the extra complexity that the recognition may not be perfect. I guess it really depends which is the most interesting aspect for you.

[afrancis]

I find with all the voice APIs out there, I would recommend choosing one and diving in. One of the skills is getting comfortable with the interactions between the voice API and the back-end.