My plan is to primarly play out of the normal formation and cycle through the others to pick up a few other formations with plays that i love that i can sprinkle in to my playbook.
For the conversion - I believe this is only an issue if you are simming games as that seems to rely heavily on OVR rating. I have done enough moving players in the past that I am not too worried about the lost rating on conversion. This is also mitigated by picking athletes to start with (HB/WR athlete for A backs, HB/RB athlete for QB, etc). The one with the largest negative is the TE>WR, but if you get a decent recieving TE he should do just fine at WR.