Removing impurity from the door

Q: If there is visible impurity from along time ago and was never cleaned what should I do? And how would I clean it since its on a closet door because I can't pour water on the doors. Also if I use a soaking wet tissue, if the water while wiping falls on the carpet will the carpet become napaak? I avoid those areas of impurities so after I do wudo and close the door where the impurity isn't there will I become napak? I have read namaz many times before after doing so, did they not count?

Becoming a shia

Q: I have committed zina twice. I repented once after the first time and made the mistake a second time. I'm not sure if my repentance will be accepted by Allah Ta'ala. After I committed the crimes I became a Shia Muslim. Have I taken the wrong path? I really need help.

Wearing white gold and platinum

Q: I will be getting married soon Insha Allah. I know that men are only allowed to wear silver and women are allowed to wear gold and silver. However what I wish to ask is that is it permissible for men and women to wear white gold? Is the law of white gold any different from the law of normal gold? Could you also explain whether men and women are allowed to wear platinum?

Missing a waajib in qadha Salaah

Q: I know that if you miss a waajib in prayer, you must perform sajdah-e-sahw, and if you fail to do so, you should repeat the prayer, so long as its time remains. However, once the time for the prayer is over, the prayer is not to be repeated. What is the status of missing a waajib act in a qada prayer? If you miss a waajib in a qada prayer, and you failed to perform sajdah-e-sahw (or you performed sajdah-e-sahw incorrectly, i.e. you made only one sajdah), do you then have to repeat that qada prayer? Is it merely recommended to repeat that qada prayer or is it waajib to repeat that qada prayer?