The data will not migrate, you will have to create a new design in Schematics. Plan on keeping AutoCAD available for a while to view old designs (if you do not have PDFs or other viewable files for them). We have been saving PDF copies of our designs from our previous schematic sketching software and our Pro/Diagram files so that they are viewable without the software.
We are talking with an outside vendor to do some redrawing of designs that we know will be the starting point for new revisions. This could be done in house from our PDF copies but is being done to save our designers time in the migration process. They will have a starting point ready for their new work instead of needing to start from a blank design.
I will echo Antonius's comment about getting a consultant to help plan your system. We are using a hybrid system (it combines the schematic and wiring diagram into one design sheet) with a lot of automation to make the designer's daily work easier at the expense of a lot of one time items for the librarian. If you go from PTC's literature, you will not see this in their suggestions.
The cost, compared to the time saved, was well worth it.
The biggest thing that will hit you is that you will need to develop a library of parts. The PTC tool for sketching them is much maligned but quite easy to use if you ignore 90% of it. We tried using DXFs from our old software (never intended for this use) to create the start of symbols but it generated a large number of entities that Schematics could not understand and caused issues trying to edit them. Our best results was just printing the old symbols with a grid turned on and using that to create parts that could be used in many symbols.
One result of this is that having to redraw the symbols completely gave us a chance to make the new one consistent. Our old ones were created on the fly by various people and didn't quite match and some were just plain wrong.
