scenarios will all have a Kill point component for the primary, just with things like headhunter in one scenario and additional rules in the third scenario.
LOW/Primarchs/Titanics will be KP based on wounds : 0-12 = 2 KP, 13-24 = 4 KP, 25+ = 6 KP
Every mission will have different secondaries that are things like first strike, linebreaker, slay the warlord + 6 more
Every mission has a paint scoring component and a sportsmanship component. You do NOT have to be fully painted to attend the tourney or to get points for painting, however to get higher points on painting you need to be fully painted. (just showing up with a fully painted army gets you 3 points out of 5). Sportsmanship is out of 4... but with VERY clear definitions as to what each level should be.
there are no upper limits on primary. It's based on how many things you destroy. You knock out 18 KP worth in a mission (remember some things are weighted more on certain missions) you get 18 points for primary. You kill 1 KP, you get 1 and have to hope you get a ton of secondaries are a great opponent and painted your stuff.
all points are cumulative throughout the day, and the last scenario you're all but guaranteed to get a bunch of KP due to the special rules involved.
There you go... that's the premise for the tourney. Even bringing a low model count army (ie: knights) doesn't necessarily mean you won't be giving up a ton of KP, and having less units MAY make doing some secondaries harder. Having a scardy cat warlord might make some secondaries harder as well.
Think to yourself... what kind of tourney would make KHORNE happy... and you've basically got it.