I think the number of stats dpends on how long and diverse a game is. A short, linear game like Choice of Dragon needs less stats than an epic like The Lost Heir trilogy or Guenevere.
If you want to get your game official and not just hosted, you need some stats that impact the events of the game and the outcome of choices, otherwise it might be rejected as official game as happened with Divided we Fall.
As to which stats should be shown and which should stay hidden, as a rule of thumb all stats that show things that are the MC should know about like abilities, skills, knowledge, equipment or money should be visible while stats reflecting things that are less obvious like the relationship values or health of party members may be hidden or not. Stats that might spoil things should definitely stay hidden.
I’m not sure what you call ‘character opinions’ , can you explain it please?