Hi! Backpages, for the purposes of this jam at least, are intended to be 'extra stuff' like GM tables, item and spell lists, etc.
Characters sheets - if they are even necessary - don't have to be on your main page as they would take up a lot of space. You can have reminder text on character sheets but I'd avoid brand new rules.
I would ask the question 'can this game be played with just the front page?' and if the answer is yes, you're good.
That said, if you think you have a good, interesting, or innovative reason for having the core game across two pages, go for it. And characters sheets could have new information on them if you want (I'm thinking of PbtA and FitD playbooks as a good example). The main thing IMO is people aren't submitting 10 page PDFs of rules.