1: you will face only people that were either KoG previous season or have reached DLV max, in other words you will face the best of the best. so even small edges will be of major importance. the world champion of previous KC cup had a winrate of 61% with a sample of almost 500 duels, so 61% is a HUGE amount. i had a winrate of 52% myself, which is imo a good...
winrate as well since i wasn't usuing the best deck at the moment (which was vampire), i was using anki deck.
so actually everything that's above 50% long term is a good winrate.
2: the first stage is based on getting lv 20, which is based on wins vs losses (example +3 wins will rank u up). the second stage there is no rank up. but instead you will earn/lose points, the theory is actually the...
same idea, but the point system means you earn about 1000 points for every win and lose about 1000 points for every loss, so since there is no actual rank system, the main difference is that it's a long term grind. because of the luck factor and the point grinding, you need a positive winrate (above 50%) and you need to play as much as possible to grind as much points as possible.
rewards are based on your worldwide ranking (except for the 2nd stage of the WKC reward, which is continental), instead of moving up. in other words only your end total matters. that being said, the reward are mostly very lousy unless you are getting extremely high, in that case you get lots of tickets, but as mentioned earlier, getting extremely high against the best opponents is extremely hard