Leafs really can't afford Konecny this season, and then they don't have enough cap for necessary signings next season.

They definitely can afford him this season and next. He clearly fits this season ^
- Cap will go up at least a million but i wouldn't be surprised if it's more.
- 5.75m coming off the books in Kerfoot and Engvall next season.
- Bunting probably in the 5m range
- Samsonov probably won't get much of a raise.
- Kampf will get his bump but I think under 3M cap hit
- D is set for next year
- And the rest of the roster can be filled with <1m cap hit players

Sorry you're math is wrong. So if Engvall and Kerfoot goes....that. 5.7m...minus the 2m in replacements. So the that's 3.7m plus the 1m cap increase . Let's say five million. Kampf, Holmberg, Timmins, Bunting. Yeah that might cover the 5m, but still a 20 man roster is not workable.
Heck your 20 man roster posted is just barely under the cap 82.5m is barely under the cap.

Being barely under the cap is the point. The Leafs went into this year over the cap.
If you spend some time playing around with the roster, it's very easy to make it work.
https://www.capfriendly.com/armchair-gm/team/3827443