245/50R18 unless you can -1 to 17" wheels depending on the model you ordered. 28i yes, 35i more than likely no.
BMW will more than likely be recommending Dunlop SP Winter Sport 3D Run Flat or the Dunlop Winter Sport M3 Run Flat.
http://www.tirerack.com/tires/tires....i&autoModClar=
http://www.tirerack.com/tires/tires....i&autoModClar=
http://www.tirerack.com/tires/tires....i&autoModClar=
http://www.tirerack.com/tires/tires....i&autoModClar=