Q1. Allah is absolute independent and we are dependent and interdependent. Therefore, we need the reward and not Allah. He gave us Salat out of His unconditional love for us
Q2. We all need salat naturally because salat takes care of our natural needs such as providing peace, showing gratefulness to our maker and Sustainer etc.
Not doing it means being ungrateful to our maker. This is when the sin comes in. Common sense dictates that we should always be grateful to those who have done something good to us. The best of all is Allah. Therefore salat is away to be Grateful.
Q3. Prayers is not just to avoid Hell. More importantly, it to connect with the world of the unseen and reality.