1080p is Full HD and the best choice for watching on a TV or a large screen. Expect around 35 MB per minute.
720p is HD and looks sharp on phones and laptops at roughly half the size.
480p is the light option for slow connections and limited storage.
Why MP4 and not WebM
MP4 with H.264 plays on essentially every device, player and editing program. WebM compresses better, but takes far longer to process and some players will not open it. When in doubt, MP4 is the safe pick.
Video and audio come separately
Streaming platforms store the picture and the sound as separate streams. woconv downloads both and joins them into a single file, so what you get already has audio.