The higher the offset, the closer they are into the car. The lower the offset, the more they will stick out.
The standard 18inch BBS sports which i had on my car to start with were around the ET50or ET52 mark.
I am purely telling you the set up which i had and how it sat, Simple as.
i was 19, 235 tyres, ET45 - wheels sat pretty much in line with the rear arch. on the front, if you looked straight at the car you could see they were sticking out a few mm. They would only scuff when hitting dips on the road.
Your's being an even lower offset (sticking out more) i would presume that they would not only look a bit daft, but cause more rubbing problems.
Here is my car just now, ET45, 225 tyres - as you will see they sit just about inline with the arch.
and here it is with the ET45 235's
I would put money on your car rubbing on dips as the wheels will stick out further and if u came to lower it you would probably get big rubbing probs.