Let this season play out and see what you have. In the offseason they will have a better sense of where the organizational depth is and when those prospects will be ready.
Schierholtz looks like a keeper already. Ishikawa less so, but deserves a little more time. He's starting to turn it around a bit after hitting .190 with zero HR in the first month.
It will take more than one player to make this into even an average offense (a slugging LF and a middle infielder who doesn't suck at the minimum) and getting multiple pieces will not be easy midseason.