These three issues are kind of connected. They're requesting you your Google account email so they can associate your account with their private beta (available in the Chrome store) and let you install it from the Chrome's webstore.
You can go the other way around and "build" it. Just clone their repo and point Chrome to the cloned directory so that it knows that there's an unsigned extension there. Done.
Yes. On a mobile. We might have a different interpretations of the GP's requirements.
Given that they replaced Lync/Skype for Business™ I assume they ideally want a comparable offering: Voice and chat for a number of platforms.
Signal would give you voice on mobiles only and chat on mobiles only, ignoring the Chrome App beta thing.
I might be entirely wrong, but I assumed that the GP chose Telegram for now due to the multi-platform support (chat on all platforms, replacing Lync/Skype in that regard completely). If that is correct, moving to Signal would be a trade-off, exchanging multi-platform support for voice calls. It's not a solution, it's a different subset of Lync's/Skype's feature set
Once on of your contact uninstall Signal without disabling it first, you will have to long press the send button EACH time you want to text them. Annoying as hell, it made me stop using Signal.
