Oh, definitely vertical format is important! You can make your comic in a page by page format, but you should definitely reconsider reworking it to fit the scrolling format! It can help with pacing and most of the viewers on the site expect or have a better time reading it that way.
I honestly love making my pages that way cause i get to add movement and pace out actions and dialouge.
Also I learned the hard way, that a simple easy to read font is good as well. Basically, most webtoon viewers read on mobile phones and tablets, so the format must be simple enough to read.
