First point, KC is the only VCT team (tier 1) that offered a Head Coach position to Engh. KC entrusted the project to Engh, allowing him to completely rebuild the team in his own way. One of Engh's objectives was to create a team that was exciting to watch, with a very aggressive playstyle.
The project revolves around Magnum: according to Engh, he is one of the most underestimated players in the game. An important piece of information: Magnum was eager to become an IGL, and he was even willing to turn down VCT offers to take on this role in tier 2. We don't have much information about Zeish's presence as an assistant coach, but apparently Engh conducted some sort of interview with him and the vibe is quite positive. There's also no information available about Youenn, the performance coach (ex Fnatic). We know they conducted about a month of trials to find the right players.
Engh's second choice is N4rrate, he says he was very impressed by his way of thinking and creativity. He doesn't mention his mechanical skills, although they're generally considered very impressive (such as when he performed the trials with over 100 ping and apparently dominated everyone). Then, he decided to keep Shin (even though he still had to go through the trials, his place wasn't guaranteed), who will return to his main role: Smoker. Engh emphasizes that he believes there are very few good Smokers in Europe and that keeping Shin was a fairly obvious choice.
For the duelist role, they tested four people and then decided to try someone else who had been spotted as a young talent by Zeish: Marteen. Apparently, he outperformed everyone during training and has tremendous potential. For the last spot on the team, Engh decided to let Magnum choose, giving him the sole instruction that it had to fit the team's very aggressive playstyle. Magnum watched trial videos and immediately chose Tomaszy, who therefore transitions from duelist to Sentinel.
Engh announces that he doesn't really have any expectations for the kickoff tournament (which can be understood given the shitty format), but he wants to use this tournament to "find the team's identity". I'm not sure exactly what he means by that, but basically, he already expects the playstyle to be different in practice and in official matches.
A bit off-topic, but for your information: all the players who joined KC agree on two points: they joined KC because of Engh's presence and the big fanbase (we could easily say the largest in VCT EMEA).
To summarize, the roles:
Marteen -> Duelist
Shin -> Smoker
Tomaszy -> Sentinel/Viper
N4RRATE -> Flex
Magnum -> Flex (IGL)
Sources:
https://www.youtube.com/watch?v=2fDui4016SM
https://www.youtube.com/watch?v=DbYD_QUvx_c
Random streams of players and Zeish
Discord