When healthy, the Habs don't even quite have $2.5million in cap space. As of right now, with guys injured and others being called up, the team only has $757,649 in cap space. Any trade the Habs make would need to be in line with the salary cap, so it's not an option to trade just prospects and draft picks for roster players (unless you're also proposing to put roster players for the Habs on waivers).
Hage for Larkin? Not gonna work unless you can clear another $7,942,351 in cap space. That means either Hutson or Dobson is gonna need to go the other way in that trade, too. Or two or more other roster players.
You want Konecny? He comes at about the same cost as Larkin. The Habs are gonna need to clear another $7,992,351. Even trading any one guy on the first line (Caufield, Suzuki, Slafkovsky) won't be enough to get the trade done. You'd need to throw someone else in the mix on top of any one of them to make the trade happen. Or, again, trade either Hutson or Dobson one-for-one for Konecny.
You want the Habs to trade for Elias Petterson? You're also gonna need to clear another $10,842,351 in cap space to do that. No one Habs player has that large a cap hit, so you're gonna need to pick at least two roster players to go the other way in any trade you propose, not just draft picks and prospects.
Source: https://puckpedia.com/team/montreal-canadiens