sunnats of salaah

Facing the palms towards the qiblah when commencing salaah

Q:

1. When starting salah, do your hands have to be facing qiblah?

2. Will salah be valid if you start salah with your hands facing inward towards your head? One time my imam for salatul jumuah started salah and I think his hands were facing inward. What should I do in such a situation if my jumuah is invalid and I am going to have to wait for second jumuah or go catch jumuah at another masjid?

Sunnah method of Salaah

Q: When you perform salaah, when doing takbeer to start, should we look up or down? And after raising from rukuand saying "samirallahhulimanhamida", some says you have to say "allahumma rabbanawakalhamd" and others only "rabbana lakalhamd"? Which one is correct according to sunnah? And is it obligatory to say it? If i did not say it, are all my prayers invalid?