How should one pray two by two rak'ats of naafil?

As-Salamu alaikum brothers and sisters, i heard that Duma should be prayed two by two, that's saying the Salam in each second rakah, does that mean that (1) you have to announce (by heart) the intention and takbir l-ihram again? (2) and are witr and qiyam al layl also two by two? (3) and is saying Salam after each two rak'ats fardh? Because I prayed 12 rak'ats of duha with only saying one Salam. (4) and after you say the Salam, are you able to move to another place and finish the prayer? Jazakum Allah khayran...