1: Yes, you'd need two different Gmail accounts to do that; each account with one Google Voice phone number. Keep in mind: you are only entitled to one free Google Voice number per personal phone number submitted as a "claim ticket".
2: No. If all you want is bare-bones Internet VoIP telephone service, then get that service from a different provider, such as
voip.ms or Callcentric.
3: Yes, but it has relatively short range.