If I auto-forward my voicemail (from my non-GV number) to Google Voice, do I need Verizon's Visual Voicemail service?
No you do not. Google Voice is what you will use for visual voicemail. The app is already on the droid. And with Google Voice you can get transcription to text for free. It is not 100% accurate but gives you a good idea what the message is about at a glance.