If you want your fantasy league to resemble real NHL, then maybe you should do the following:
1.A game period should last 2-3 days (I suppose depending on the schedule), not 1 week.
2.You can field 1 starting goalie and 1 backup, whose stats count only if the starter doesn't actually play.
3.You can also field 6 D, 4 LW, 4 C and 4 RW.
4.You should probably have a nice bench/farm team pool (Yahoo allows no more than 30 players, so it would be 10 reserves).
5.Every starter should be able to play only 1 game per game period. If his real team plays more than 1 game during the game period, you pick beforehand which game's stats will count for the player.
Then and only then, no streaming will be necessary. You can probably limit free agent signings to 1 per week or so.