Please find answers to first three questions here in this answer by office if his eminence:
http://ijtihadnet.com/childrens-obligation-toward-their-parents-according-to-ayatollah-sistani/
Re 4, no it’s obligatory. Re not marrying someone it depends if it’s a girl or a boy, and the reasons for parents not allowing the marriage
5. Try as much as you can to make them understand. Do not disrespect them. But sometimes they will not accept and that’s the nature of human beings