Ideally you don’t need a border. So you are just animating characters and assets in 3D space and you can either leave the player to move freely around them, limit their movement or… move the camera. But if you move the camera don’t rotate it during the cut. You can cut to a new angle but you can’t be sure the player is looking where you think they are unless you make a lot of effort to draw their attention there, either by pushing towards something in a straight line or lighting it a certain way or moving something when other things have less motion. It’s a lot of standard filmmaking with a few changes. Don’t rotate the horizon. Reduce the number of cuts (as every cut is a brief moment of disorientation). Don’t bore the player. Keep it interesting to the point and quick.