You must obtain the waiver of

2 years service to your home country first if you want to change your J-1 to H-1B later. You can only work under OPT if you are going to work in a different institute from the one of your J-1 sponsor. You cannot work under J-1 for someone who is not your sponsor unless you get the waiver first and then get a new J-1. It is almost impossible from practical point of view.