Receiving one's salary on one's zakaat date

Q: I am sahib-e nisaab Alhamdulillah, however my regular monthly pay mostly gets consumed by the next pay date. If I receive my pay on the zakaat anniversary date, should I include that pay's amount while calculating zakaat, or whether I should calculate the zakaat on my remaining assets after deducting the following month's expenses? 

Also, what sort of future expenses are permitted to be deducted before calculating zakaat on one's zakaat anniversay date?

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?