Why did you create all those duplicate posts? It's bad forum etiquette, unless you're a spammer.
Your entire proposed/actual solution is a very bad idea. The mostly-free, consumer version of Google Voice is intended only for consumer use, not for business. It has no direct support from Google, no guaranteed service levels, no 911 calling, and yes, things do break. You'd be betting your entire business on it. Aside from that, it's a violation of Google's terms of use to obtain multiple phone numbers for your business.
Google now has a true, business-class version of Google Voice for G Suite customers. You can have as many "seats" with phone numbers as you need, it's supported by Google, has 911 support, and it includes, or will include, most of the features you listed. It works with the Poly VVX x50 series IP phones. It does not work with any of the legacy OBiTALK products. By the way, the 1000 series phones are outdated and will be discontinued when supplies run out.