All of those characters are needed for something later in the game so your resources aren't being wasted, but I agree with the two posters above me that you should probably prioritize Bossk as he'll be a key element in almost any bounty hunter team. Also, his ship is widely regarded as one of the best ships in the game and is easily the best tank in fleets by a wide margin.
With Greef, Mando, Bossk, and almost any other two bounty hunters you'll have a solid team to unlock Chewbacca if you haven't done that already.
