You gave a subject, a thema. I recommend some variations, and maybe I will try to write them. Well, I am not a professional composer, but eventually I have some ideas.
Regarding the rules of harmony, etc., all this is not important at the moment. All that counts is what you hear with your inner and outer ears. For instance, the last chord seems quite convincing to me though it is a 4-6 chord. A question: Which sort of a teacher do you have? Mine in my childhood could not deal at all with my first trials to put musical ideas on paper. Try to talk with your piano teacher about your creations, and if he or she is not able to deal with them, leave!! and look for someone else.