IMO, just use the language your know it well. It might be a little bit off topic, if you are going multiple platforms development now, such as backend, ios and android, will you go native now? or use cross platform languages? :D
For (2),
> Our goal is to be able to install a package using Puppet, Chef, CFengine, or something else that puts all of your code in a standard location every time, on every server.
For (3), I think it can be solved by some database migrate library?
I am so scared moving all my "right" to my phone. If my phone is stolen, that guy can browser my visiting sites history, and then try to use clef to login, payment...