A number of e9x M3 owners who track their cars prefer the square set up in order to be able to rotate tires, as well as neutralize the car by reducing the induced understeer from the staggered setup. You can easily fit an 18x10" ET25 all the way around on your car with the 275/35/18 tire size with the OEM suspension, and most aftermarket suspension. Additional negative camber or fender modification is not required with this wheel and tire fitment, though some people do add a little more negative camber in the front to help with the turn-in. You will not be able to roll your fenders as they are plastic on the e92 M3.
There is an exception to the 18x10" ET25 squared setup with 275/35/18 tires fitment if you have KW Clubsports on your M3. The square setup will still work if you remove the helper spring from the front struts, otherwise you would need to put at least a 5mm spacer in order for the wheels to clear your spring perch. KW's helper spring causes the spring perch to sit lower than normal, and will thus interfere with the tire. If you choose to not deal with spacers at all, but would still like to do a squared setup on your M3, you can either remove the helper spring to move the spring perch up, or go with the 18x9.5" ET22 squared setup with 265/35/18 tires.