IMHO the best way to become a competent photographer or videographer doing underwater work is to first become a competent diver. This takes many dives under many different conditions. As said previously, having excellent buoyancy control and body awareness in the water is a must and probably should be learned long before you take a cam rig down with you. Have fun learning to dive first. Your OW certification should be looked at as only a learners permit to now go out and safely learn to be a competent diver. I used to tell that to my dive students back in the day just as my friends said to me "Take the OW course and then come out with us and we will teach you to dive', and they did.
By the time you have that extensive diving experience under your belt both during the day and night, in good conditions and poor, you will have made dive buddy friends who are into photography or video. They will do a better job of teaching you than some silly PADI course that is there only to take a few more bucks of your money. And its not just PADI either, it appears that most of the dive agencies are creating these money making courses. First you take their advanced 'Getting your right fin wet' course and then their 'Getting your left fin wet' course. Just nonsense.
You will also find that you will gain a wealth of knowledge right here on Wetpixel and it will prove to be a very valuable resource. Meanwhile, as you are learning to dive, while topside you can take a class in Photoshop or Lightroom or an editing NLE of your choice depending upon your aspirations. Then when you are ready to go in the water with a rig, you will already have the knowledge and skills to work with what you've shot.
Good luck to you in your endeavors,
Steve