Becoming a software engineer

Q: I am interested in becoming an apple software engineer but is it halaal or harm for work there? Is working for a company which sells computers, laptops, phones is halaal or haraam? If I sell a computer to a buyer if that buyer uses it in any bad ways will I get sins?

Filing one's teeth in the state of janaabat

Q: Can a person in janaabat (sexual impurity) do teeth capping and teeth filing? Will the person become pure (free from sexual impurity)? If ghusal is done after teeth filing and teeth capping, does teeth filing and teeth capping in janabah (sexual impureity) have any affect on purity after ghusal, will the person be pure to read namaz after ghusal. Please help me because thinking all this I am going mad.

Secret nikaahs

Q: A Muslim man leading a happy married life, but out of sympathy want to marry another widow woman, and give her a life, but he is doesnt want his first wife to know immediately about his decision of taking up another wife, but later on after an year he would slowly let know his first wife know about the second marriage, so is this cheating? Will his first wife curse the second wife? Should this widow marry this man? Is she becoming a reason of pain for his first wife?