On a team rostering 20 players (4/4/4/6/2), you are pretty much an NHL team, with an NHL league that is only half the size (14 vs. 20).
So... for me, it should be similar to what the NHL would look like with half the teams.
So, instead of each team carrying maybe 3 young players, maybe you carry 1-2.
I personally don't like carrying rookies on a pro-roster unless they are top 3 picks.
If you don't have a farm, the players like Strome/Forsberg/Grigs should be carried by teams that are rebuilding or out-of-contention. They aren't fantasy relevant players for the coming year.
My answer: TWO.