The offset of your standard wheels are ET35 as far as I know (I may be wrong though) so if you were to get a new set of wheels that had an offset of ET45 for example, the wheels would sit closer to the wheel hub by 10mm and most likely rub on the brakes and shock absorber. On the other side, if the new set of wheels had an offset of ET25, they'd sit further away from the wheel hub by 10mm and risk rubbing on the arch lip if you went too far. So basically, the higher the number is for the offset, the closer the wheel will sit to the hub and the
lower the number is for the offset, the further away it will sit from the hub. Does that make sense?
To sum up, when fitting wheels from a car made by a different manufacturer with a PCD (space between bolts) that doesn't match your own, it's best make sure that the offset of them is
lower that your current ones as you'll need to remember that any PCD adapters will be at least 20mm thick. I would say personally that you should choose a wheel with an offset no higher in number than ET55. This should clear your brakes (depending on the spoke design of the wheels) with a 20mm adapter and make the wheels sit in the arch.