Salaah

Joining salaahs when travelling

Q: Is it permissible to join the salaahs when a person undertakes a journey and is a musaafir? 

For example, you are leaving a country and it is zuhr time, so before the flight, you join zuhr and asr? Or you visited a country and you go to a shop and maghrib time sets in, so you read maghrib and esha together. Is this permissible, and if not, does one get a sin when they do it?

Performing salaah with impurity on one's body, clothing or salaah area

Q: Is someone who prays 5 times a day consistently with proper wudhu but knowingly and intentionally prays with impurity on the body, clothes or prayer area rejecting the obligation of purification, would this person be considered a disbeliever and be in hell forever? 

Is this person performing wudhu for each salah clearly showing that he is NOT rejecting the obligation of purification?

Imaam starting the qiraat while one is reciting thana

Q: In Prayer behind the Imam, if the Imam starts reciting whilst one just started reading the Thana and he was in the middle of saying اللهم in the Thana but the Imam had already started so he just finished saying Allahumma then he stopped reading the Thana, 

1. Would the prayer be valid? 

2. Would he have missed a Wajib and have to repeat the salah for missing a Wajib?