Q: Is it a Bidah to shake hands and make salaam to one another after the Salah?

Q: Why are Muslims allowed to marry four wives? 

Q: I am Alhamdulillah married and my wife's father is a qaadiyani. However, I am not too sure what type of qaadiyaani he is. I know he does not believe in the fool Mirza being a prophet but I think he does believe in him being the Mehdi, even this I am not to sure about. If not then he just gives some standing to him. My mother in law is a sunni muslim, how they came about getting married is because they are 1st cousins so I don't think much attention was given, the family is not well linked with Ulamas etc. At first I was not too sure how deep my wife's father was in qaadiyaanism. Initially my thinking was because his siblings were all qadiyanis he had some weakness towards it and just said he is a qaadiyani because from what I know he practices Islam the sunni way and talks very highly of prophet Muhammad (Sallallahu Alayhi Wasallam). But my mother in law came over (they live in Canada, I am in the UK) and I finally got the courage to ask her a few questions about my wife's father and from there I have become skeptical and now I am not too sure how deep his belief is. He does on occasions like Eid pray behind their Imaam but again it is because all his family are there. I was introduced to my wife so I don't know the family too well, however neither did my wife know her father had these type of beliefs as her mother always brought her up in sunni Islam.

Here are my questions:

1. Is he a Kaafir?
2. If my mother in law believes him to be a Muslim does she stay in the fold of Islaam?
3. My In laws are very kind to me so what sort of relationship should I keep with them?
4. Its difficult for me to ignore him out but I am beginning to feel some serious hatred if his belief is kufr, should I still go visit them in Canada?
5. How should my wife's relationship be with her parents?

Q: If I told Allah that he must give someone else my Jannah (something to the effect), will I be forgiven and my Jannah will not be given away?

Q: Can you please refer any hadith stating that there is no such concept in Islam to hold Quran Khawani before getting married, I need to show it to my in-laws as they want to hold a Quran Khawani before the wedding ceremony, as they say it is better to start it with the name of Allah. I personally do not believe in these things, as I know they have no standing in Sunnah.

Q: I downloaded something haraam on my phone. They charged me a fee. I broke my sim card. Hence I won’t pay the entire fee. Although it is possible to get another sim card with the same number, does it suffice to seek Allah's forgivness alone?

Q: How long can we delay to perform nikah until all the guests arrive?

Q: If someone tells me you won't get jannah or I will not take you into jannah or a Hafiz tells me I wont take you into jannah or you won't go into jannah. Or anything else like this. Will they affect me or can I ever be deserving of it being told me and then will it affect me?

Q: Should food be prepared for the nikah or only for the walimah? Must it be the cheapest possible, like fresh fruit and vegetables instead of biryani?

Q: In jannah will we desire and have human friends and go out with them and enjoy it similar to that of this world?