You pick two things before you render: what the picture does, and how long the video runs. Plus is a living scene that loops, at 1080p. Lite is a still scene with your soundtrack, and it's the lightest on your usage. Either one can run up to an hour. Lite is on every plan, and Plus is on Creator, Pro and Max. Studio usually opens on Plus (on Lite if you're on Starter), or on a shorter or lighter setup when that fits the usage you have left better, and you can change either choice before you render.
Every video comes with a soundtrack. If you'd rather have none, pick Ambience only under Music and you get the sound of the place instead: rain, fire, cafe.
Each style has its own quality setting. On Lite, Quality sets how sharp the still is: Low, Medium (the default) or High, and High is on Creator, Pro and Max. On Plus, you can finish the video sharper, at 1440p or 4K, under Resolution in Studio, also on Creator and up. On Starter, videos are Lite: a 4K still image with original music.
How much usage a video takes follows those choices. A longer video uses more than a shorter one. On Plus, Loop duration sets how long the scene runs before it repeats: Auto lets Chillframe pick, or you can set 10, 15, 20 or 30 seconds. A longer loop uses more, and so does a 1440p or 4K finish.
You don't have to do any sums. If a render needs more than you have left, it won't start, and Studio tells you before you begin. Settings → Usage shows how much you have left.
If one part of a finished video isn't right, Re-roll music, visuals or the thumbnail covers redoing that layer on its own.