So much depends on what the Blues do - they are so deep and balanced that this affects the production of their forwards.
I could see them eventually settling in to having two scoring lines and a two-way energy line:
Scoring line players: Perron, Schwartz, Backes, Tarasenko, Berglund, Stewart.
Energy/two-way guys: Steen, Oshie, etc.
I'm probably missing someone, and not factoring in Andy Mac long term.
I could also see them moving a forward for a defenseman at some point, assuming Schwartz and Tarasenko step in.