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?

Objections against the Ahaadith of Fazaail Aamaal

Q: I am troubled by a comment someone has made to me regarding the Fazaail Aamaal. We grew up reading it, and so did this person. But now suddenly, through the influence of another person, this person says that Fazaail Aamaal is a "Tabligh kitaab" which is unreliable as it contains weak Ahaadith. 

Can you please explain to me whether Fazaail Aamaal is a reliable kitaab or not.