My first take.
Considering the young age and the high skill ceiling of each individual on the team; I'd let the team run a quite loose game style with quick rotations on T-side and a pair based approach to get easier trades. An important part will be map control and therefore mainly spread out around the map rather than too heavy strat based tactics.
To ease in the team I'd let Stavn mainly play alone while Cadian and bORUP play together, since they already have played together for a while, and let the two new players pair up, since they already needs to learn pair team play and work together. If you change the pairs they need more time to practice.
I don't wanna use the Thorin coined roles, since they are 5 years old and the meta have definitely changed. So during a default I wanna keep bORUP, CadiaN and niko "mid centric" as a pack and TeSeS at one extremity of the map and Stavn at the opposite extremity. bORUPS, job will be to trade and support CadiaN (awper) while niko will play closer to TeSeS.
I expect to have Stavn and Teses to open up big portions of the map and to be fearless. Sure bORUP could play that role instead of TeSeS, but just for team dynamic I think it is easier for them to initially get bORUP to play between CadiaN and Stavn.
I also want niko to utilize his experience and therefore get him away from CadiaN so the information and calling will be as precise as possible.
CadiaN will be main awper.
On CT side I want niko and bORUP as rotations while TeSeS and Stavn will be anchors. This is perhaps not optimal for the teams. But since I want niko and bORUP to be "supporting" elements I expect them to use their utility earlier than TeSeS and Stavn.
All players will be mobile, quick and explosive, while CadiaN will mainly work with the AWP duels and therefore play a bit slower than the others.
The maps i want them to utilize will be Overpass, Nuke and Train, since these are the maps that Heroic have originally been good on and both TeSeS and niko are comfortable on the maps. I also wanna add one of D2 or Mirage so they have a broader map pool, and I pick those two as all players know these maps wellenough to create upsets and basic executes and plays.
My 2nd take, the more classical approach:
In this case I'll use the Thorin roles to fit the roster: 1 entry, 1 follow-up (aka 2nd entry), 1middle man, 1 support and 1 lurker.
The map pool are the same as in comment 1, just to make the players as comfortable as possible.
The reason for this is to get the most out of bORUP, a player who's been badly utilize ever since they signed him. He is so much better than he has been allowed to show so far.
TeSeS is a great aimer but needs proper people around him and I think it would be great if he was the one to be seen as a star player and having bORUP go in ahead of him, so he can frag out.
CadiaN will play the classical AWP middleman IGL, just like Fallen did back in the day when he was relevant.
Niko is one of the most obvious choices as support, not just in Heroic but in any top 25 teams.
Stavn is a great player and can do almost anything he wants in a map. And given more responsibility would be good for his development.