If you want to retain your subscribers then the quality of your photos and videos should be great. It increases your value for your fans and makes them continue with your subscription.
Using a great mic is very important for OnlyFans videos. For camera, you iphone is more than enough but you must have some latest iPhone (above iPhone X). It will not overkill your photos and videos.
Recently I started using G7X II mic with my iPhone that gives best results. I have also used Canon 5d Mark for some outdoor OnlyFans videos. Use of gimbal is suggested if you make some moving videos.
This all makes my OnlyFans videos crisp and sharp and most of the fans enjoy these kinds of videos.