How much power is appropriate for indoor photography lights?

30 square meters, I suggest you have three light areas, 300W 400W and 400 W will do. If there are four lights, I'm afraid you can't turn them on, but it's useless. Lights will affect each other. In view of the small studio, I suggest you paint the top, prepare two large foam boards, and use reflected light to shoot more. Conducive to modeling, and leave room for props.