Nikaah & Marriage Issues

Equality between wives

Q: My wife said that she will let me have a second wife if I increase her allowance from 5 to 10 000 a month. If I enter this agreement with her before I marry, do I still have to give my second wife the same amount in being equal or can I give her a normal allowance of 5 000?

Having many children

Q: In Islam, it is recommended to have many kids and offspring, but, the increase in population is also a sign of the coming of the day of judgement, so does this not contradict? A good command which represents the coming of bad days?