The term "page" can be confusing because it could refer to a webpage and/or a page of your comic.
Regarding your question, create a single paid project on Itch. Anyone who purchases that project can download all the files and updates you upload to that project without paying anything else.
That is, you can update your comic's file (ebook, PDF, zip, etc.) or even upload each page of your comic as a separate file (I don't recommend this), and your clients will always be able to download the latest material without any problems.
Be careful, if you set the project as free on Itch and then set a price per file, it could be complicated to manage; it's best to make your project paid.