Qasar Salaah and Full Salaah

Q: When traveling for 2 nights and you pray as a musafir then you realise that your staying longer than 16 days. Do you have repeat the namaaz you missed during the first two days?

Q: A person travels to a place that is safar distance and intends staying there for 10 days. After 8 days the person changes his intention and intends staying for another 8 days. Will the person read full namaaz or will he be a musaafir? What about the salaah that was performed in the first 8 days? Will he have to repeat the Salaah?

Q: If while traveling, I performed a Salaah without shortening it, is the Salaah valid? Am I in any way sinful? For example, I performed four rakaats for Isha instead of two rakaats, while traveling.

Q: If one want to travel to a city 150 kilometers away from the city I am living and I want to stay 20 days in that city. Do I have to make qasr during travel (i.e. when I leave my city until I reach the city where I am travelling to) but once I have entered the city I must pray again full?

Q: I live in Morocco but i own a holiday flat in Portugal which stays empty most of the year, when I go there am i musaafir?

 Q: If a traveller leaves his home for the airport (approx. 25 km away). At the airport, will he have to read qasr salaah or full?

Q: If a person on safr performs salaah alone and intentionally performs full Salaah, will he be sinful?