I have no idea what your startup is, but are you sure that you're going to be dealing with people who are working at churches, rather than congregation members who volunteer? Most community organizations -- churches, kids sports teams, amateur orchestras, etc -- will include someone who is technically savvy, even if the priest / coach / conductor / etc. doesn't know how to use a computer.
So, to really answer your qustion, I think it depends on what your startup is. If it's a B2C company that really only needs its own number for support issues and whatnot, you're probably good with just a GV account that forwards to your cell phone. If it is a B2B company though that needs to sound established and professional, I'd consider setting up an 800 number with a multiple-line answering service like Grasshopper, even if every line only forwards to your cell phone for now. This also makes it very easy to scale once you start hiring people.
There is simultaneous and sequential group ringing.
Conference bridging with up to 8 participants.
Each user/phone number can also configure external phone numbers to forward to.
Finally, you can create an unlimited number of "automated attendants" for your "press 2 to sound like a big business" scenarios. Along with nested menus to drill down to the right person/voicemail, if your needs are more complex.
If hosted isn't for you and you are willing to get your hands dirty, try the open source FreePBX.org for on premise build out of the functionality you've described.
Disclosure: I am on the phonebooth.net product team and are the primary contributors to FreePBX.