Kufr

Questioning Allah Ta'ala's decisions

Q: One of my Hindu friends asked how God decides if someone will be wealthy and others will be poor. Similarly, how will someone be born healthy and others disabled. etc. Is this decision randomly made by God or is there some logic behind it? I understand this life is a test but why do some people have relatively easy tests and others really hard tests?

Renewing one's Imaan

Q: I recently discovered that some of my past actions were kufr and I sent some messages containing shirk. I have sincerely repented and vowed never to do them again. I made a general taubah regarding all my past actions then recited kalimah.

1. I would like to ask if it is necessary to repent specifically for each action as all I have thought about since is remembering specific kalimat I said. Do I need to do tajdeed e iman again if I remember those past actions after making general taubah?

2. Also do I need to perform ghusl after tajdeed e iman?

3. Can tajdeed e iman be made whenn one is junub.

4. What about my prayers that I said while not realising my kufr?

Doubts regarding one's Imaan

Q: I suffer from doubts regarding many things. I am constantly remembering jokes and statements I made in the past that may have been statements of kufr. I have recently read about people singing certain songs that may have taken them out of the fold of Islam. Alhamdulillah I do not listen to music anymore. However I remember listening to and singing the same songs many years ago. I did not know the meaning of these songs at the time. I am now doubting the validity of my nikah and legitimacy of my children due to my actions prior to and after nikah. Is my nikah valid if I have commited these actions prior to nikah?