Welcome!
What kind of help are you looking for? Are you not pleased with your yogurt, what's wrong with it?
I don't add milk powder to my yogurt. Why do you add it to yours? Is that the way the recipe is written, are you trying to add calcium/protein, trying to thicken the yogurt?
Yes, less or more starter will affect the finished product. Try to use the specified amount called for, usually 1 T. yogurt per quart of milk. Do not use more yogurt culture than that.
I will try to answer more questions for you, once I know what your issues are.....but I am about to be squopped by a rain storm and fully expect to lose internet connection..