Weight increase over sedan: 150 lbs.
Weight distribution: 49/51 (sedan 50.2/49.8)
Drag coefficient: 0.33 (sedan: 0.29)
Kneeroom in rear increase by 0.8 inches over sedan
Cargo spce: 25 cubic feet w/seats up and 60 w/seats folded
5-series like rear hatch, glass open separately
Base price: $29500
Suspension stays the same, except for some tweaks to the springs for the extra weight.
There will not be a 328i version, but maybe a 330i version in the future. An iX version will follow the 323i a year later.
For more info read the article in the November Car and Driver.