If you are not going to need sound a basic t-1 will do the trick. I think the Atlas locos in ho are designed like n-scale locos with a large 2 piece frame that encloses the motor between two sides insulated from each other. Each side of the frame is a defferent polarity. If I'm remembering correctly, you will need to insulate the motor and lights from both sides of the frame, and wire the decoder per instructions to pick up track power from the frame and then allow the decoder to feed power to the motor & lights.
