Robsond

Currently I have original 235/45 17" Sport Suspension.
Trying to get above 255 on 18" rim.
My concern is:

1. if using 255 width it will stick out a little
(bulging out from underneath the carpet covering) depending on rim width ?

2. 8" or even 8.5" wide, so when you lay it flat, it will be an inch higher than stock ? Will it rub

3. Anther question is have about offset. In general terms the lower the offset the more the wheel will "stick out." A 30mm offset wheel will sit out much more than 45mm offset wheel. Therefore, bringing the wheel closer to the
wheel well/fender lip.

4. can I always roll the fenderlip, is it recommended will it ruin my car ?
(for about $100 at a body shop)

5. I know there was someone on that board that used 265 on 19" but I cant seem to locate him
6. It has to RUB if there is a huge load in the back of the car ? Wheels will be forced to hide but they will not, that will cause rubbing of the fender ??

Audi S6 has a nice set of 255 tires on 17 rims...
What do you think ?
I am not considering anything else just 255 witdth