I personally wouldn't do it. Eberle and markstrom are gonna be future studs for sure. Hedman too for that. Tarasenko will take longer to be worthwhile.
While I understand that adding these guys will give you a push, you have to realize that now that kovalchuk is beginning to produce, that is basically an added player to your team in itself.
I am not opposed to selling some future to win now, but I would try and seek a smaller deal. Maybe try and get just one of Richards or Lucic. And attempt to do it without giving up eberle or markstrom. I assume they will have cheap salaries in your league.
14 team Fantrax H2H keeper league
G, A, P, SOG, Hits, Blocks, FOW, - W, Gaa, Sv%, Svs
C - Crosby, Tavares, Kopitar, Toews
LW - Hall, Giroux(C), Vrana, Gaudreau
RW - Pastrnak, Kane, Stamkos(C), Kubalik
D - Burns, Murphy, Morrisey, Cernak, Whitecloud, Chiarot
G - Mrazek, Campbell, Brossoit, Greiss
Bench - Middlestat, Wennberg, Perron, Olofsson, Schwartz, Atkinson, Yama