What do you mean by "vanity phone number"? I was not aware that GV let you choose anything you want.
As far as options, you can leave GV as is, and just set it to forward your number to an alternate phone, either voip, landline, or a cell phone. For outgoing, you can place a call from the GV web portal or call into your own voicemail and place a call from there, both options would show your vanity number as the outgoing caller id. There is no charge for either, assuming you already have another phone line to use.
Or, you could sign up with one of the many voip providers on here that will let you spoof your outgoing phone number. You choose based on your needs, usage and pricing.