I like what you pick up but not what you're giving up.

Smith has been playing wing for OTT and I doubt they'd want PIT to get him for a rental and a 5th. Honestly Cole is harder to replace then Smith and I hate to pick up another NTC.
Merrill is still borderline, having not played full seasons, though he got it done in NJ which doesn't have that much going for it. I pick him up as depth and potential replacement for Cole at seasons end, but Hunwick is there to replace him on my team rather then play beside him.

What are you doing with Karlsson?

Zack Smith is mostly a center who took over 600 faceoffs last season and won 52% of them. the year before he took over 700 faceoffs and won 52%.

You could use merrill primarily for depth and have pouliot in. I don't think Merrill would be over matched as a #6 defenseman playing with a stable veteran and he can skate, move the puck and is 6'3".

Karlsson is depth at center. He will probably set in at wing most nights probably rotating in among the 4th line. He has playmaking ability but hasn't popped yet. In a more speed based attack he may be able to break out more and be a diamond in the rough find.