Ok how long time does it take before the transaction is registered as valid?
Depends on the transaction fees, the no. of transactions at that time, etc.
And how much is the miner rewarded for creating that block?
The block reward right now is 12.5 BTC and the transaction fees.
How many transaction can there maximum be in a block?
Varies w.r.t. the transaction. On average (as of Nov 2017) 11K+ per hour (Source)
The difficulties increases all the time. Will we reach a point where it is impossible to create blocks (=The end of bitcoins)
The difficulties increase because the mining power is increasing. If there comes a point where the miners drop out due to increase of difficulty, then the difficulty decreases within 2 weeks. It will decrease in such a way that to make it an average of 10 minutes to mine a block.