First I would thank GOD for this opportunity and let GOD konw that GOD is always welcomed to visit my planet, so I could continue to do my best to try to serve. Ok that is it for humility
Ok you said start small, I would have went the other way, creating universes and multiple dimensions first.
The planet would not be like earth. I would create 1 million different forms of life. I would be capable of changing my form at will. I would have a sky that changes colors based on how I feel. There would be no kill of anything on my planet.
I have to be honest there would be no free will. My planet just do as I instruct. I would write many stories and created the characters and have then play the story out to entertain my self.
I would have fun at all time. I would do what ever I want to do. When I am in human form I would create people to play with. I would not let them know they did not have free will. They would enjoy thinking that they were making their own decision, while I was secretly pulling their string, because in a way that would be my real job.
If I did cause my creations pain because one of the stories I put them in was painful. I would remove the memory from them at the end of their existence. I would not want to create spirits because I think real spiritual beings should have free will and since I would not be the original creator I would not want to do harm any spiritual beings from the original creation.
I would not want the original GOD to get upset with me so I really would ask what I could do and what I could not do out of respect.
Nice question, Sorry I rambled on.