2. You have to get waiver before you can change your visa status.
3. Yes. It's pretty easy, just needs some time.
4. You can go abroad taking a vacation and come back persuing your J1 status as long as you work for the same sponsor within 3 years, like F1 and H1 visa holder. The only concerning is if you don't have a valid visa stamp in your passport, you have to apply a new visa to come back, which is pretty hard right now. Even for H1, many people have been hold for several month for a background check. This is nothing to do with your visa status.