No idea how I set it up, it acted weird at first, but...
1) I don't get txt notifications for vm - turned it off in settings
2) my VM greeting was recorded via google voice website and phone
3) I turned on sync w/inbox
4) When someone leaves voicemail, I get a notification in the status bar via gmail, and I can go into google voice and read via visual VM or listen to my messages.
5) my texting is still done via stock android messanger, both in and out... no duplicate problems or otherwise.
everything is working the way I want it too for now (I think).