Husband telling the wife "we should separate"

Q: Could you please give clarity on the issue of talaaq. If I have said to my wife that we should separate and subsequent to that we are both in agreement that our marriage is over. Will this be considered a talaq? Secondly, if i have uttered the words, I hereby give you a talaq and she records it on her cellphone, when nobody else is around, will that stand as a valid talaq? Lastly, if I have said the words and the same night my wife states that she has started spotting (starting menstruating), does it make the talaq invalid or is it simply a case of the Iddah period being moved till after spotting ends?

The purpose of purdah

Q: What is termed as Pardah ? Nowadays we see many women making pardah but the cloaks and dress that they wear are colourful and have many designs. Is this permissible? Please explain what is Pardah? Also mention quran and hadith stating pardah and the harms and punishment of women not observing the proper pardah.

Reciting ربنا و لك الحمد حمدا كثيرا طيبا مباركا فيه in fardh Salaah

Q: Can a person read the following Dua in his Fard Salaah:  حمدا كثيرا طيبا مباركا فيه after reading: ربنا و لك الحمد, in ruku', similarly can he read in jalsah: اللهم اغفرلي و ارحمني و عافني و اجبرني و ارزقني and if he is a muqtadi can he read these two dua's?