The front rotors are the same IIRC. Rears will have to be changed, which requires more then just the rotors. And yes, you will be purching 06/07 pads in the future. Subarugenuineparts.com sells a kit that comes with everything. And I know a lot of good information has been posted about the FHI 4pot conversion on this site since I did a lot of research prior to 06 on the subject.
Just FYI, this is overkill and needless unless you track (or similar) your car.
"We live for a good time, not a long time."
RIP Colin McRae