Yes, and He's eternal and immortal, therefore His rules are different from man-made rules because men are not immortal, due to sin. This is critical to understanding God's laws vs man's laws because God's laws are framed from an eternal and everlasting point of view, whereas man's laws are not.
So why did he make up this rule that says he cannot forgive unless his son is killed?
God pays the price for our sins in order that we may live forever with Him as originally intended before man sinned. He knew we would sin and die, which is why Jesus(begotten of God) was sent to die and save us from death.
Q: Why does God feel the need to pay a price for our sins and redeem us?
Because even though we've sinned, He still desires for us to have everlasting life because He's a loving God.
In human terms, it's similar to how a loving father/mother wants their child to be a loving and respectable person despite the wrong choices they make, so they'll punish them for wrong choices and discipline them and tell them why what they did was wrong to make them better and give them the best chance at being a loving and respectable person in life. In this case, with God, we're talking about eternal joyful life that never ends, which is why the punishment and discipline is on a different/higher level than mortal humans are used to.
You say only one could do that. Ok, that is the rule you think the world works by: In order for God to forgive, his son has to be killed. Again, who made that rule? God? If your God is omnipotent, why didn't he make a different rule? Why didn't he say he would forgive after a few years of community service?
See above. The simple answer is because God is eternal and immortal, he's not a mere man, though He chose to subject a part of Himself to mortality through Jesus Christ's life and death(never sinned during his life on earth) in order to save all by raising Christ from the dead and achieving victory over sin and death for us.
The reason God could raise Christ from the dead is because Christ never sinned while being a man, which means he actually didn't have to die, he didn't even have to become a man, but he chose to do it in order to save men from sin and death through his death and resurrection.
The Father and the Son work together as One to achieve God's will, which is the salvation of man to eternal joyful life.