Does itch document how they calculate the overall scores at the end?
All the entries in the jam are ranked by the average scores in each criteria. An Overall rank is also calculated from the average of all the criteria results, and this will determine with final placement/winners. No one criteria has more weight than any other. The "Overall Impression" criteria is intended to give judges a way to nudge their scores in cases where a game is more (or less) than the sum of its parts.
Just curious how the various categories, number of ratings, etc. factor in.
Only the "Game" category is ranked and awarded a winner. I know you can rank the "toy" category, but that's just a shortcoming of the itch system (I can't not rank one category). Number of ratings etc have no impact on final winner (outside of a tie, which would go to the game with the most rankings).
Any guidance on which page to use for feedback?
I am planning to use the compo page, because the game page may change over time (if say the game gets turned into a full release at some point) and this feels like more of a snapshot in time. But the main purpose is to get the feedback to the creators, so either way should work.