Qasar Salaah and Full 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?