Answer
(Fatwa: 475/L=245/TL=1433)
(1) It is haram for male and female to do nasbandi (vasectomy), hence it is not allowed as per the Shariah to do so.
(2) If the medical representatives give you something as gift without any demand then it is allowable to accept it. However it is not good to prescribe their medicine due to gift in place of some other good medicines.
(3) For investment it is better to buy some land and sell it after some years. It brings more benefit and has no harm as per the Shariah.
(4) If you practice while you are not allowed for the same legally then there is no harm as per the Shariah but in this case it shall not be lawful for you to take the allowance of non-practice. If practice is forbidden legally then you should follow the law.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband