Various masaail of Salaah

Q: Is it alright to pray behind someone sitting in the mosque? And if someone is praying right behind me, can I move or get up from from that place?

Q: I don't have a right hand index finger the one we raise in Salaah. Does this mean anything in Islam?

Q: If any person shaves his beard, will that have any effect on his Salaah? Will his salaah be valid?

Q: Ruling on a person taking drugs, when can he read or touch the Quraan and or read namaaz?

Q: At what age are children held accountable for missed prayers and sins? I read an article about it and that it starts when boys begin wet dreams and girls begin menstruation. But is there Quranic evidence to back this up? If so please add it along with your knowledgeable answer.

Q: This may sound like a silly question but it has always been wondering my mind: Are girls before menstruation and boys before wet dreams going to be punished in the akirah for missed salah/prayer? Also please add Quranic proof if you can!

Q: While praying namaz in huge congregation, if any technical problems arise like microphone switch off and followers are unable to hear the command of Imam, can any follower repeat the command on behalf of imam?

Q: Due to age, a person cannot remember how many rakaats he prays. There is no one that can remain at his side and guide him throughout his Salaah by guiding him through the postures of Salaah and informing him of what to do. What should he do?

Q: What is the significance of having a forehead mark from salaah? Why people don't have it even after praying for years? Some people have this mark only after a few weeks of praying. Is this some sign that the prayers are thrown back on the? People are telling it's a sign of hypocrisy? Is it true?

Q: Please advise:

1. Is there a link between the Fardh Salaat and Rizq?

2. Is there a link between Rizq and acts of impermissible lust/immorality?