Body shops should be able to roll and pull.
What size wheel and it's offset and how it fits will be relative to the suspension setup and the goal you are trying to obtain.
Tire aspect ratio, diameter, and width is also a factor. Even the shape of the tires shoulder will determine fitment.
How the wheel sits on the car is relative to it's offset and wheel width. Offset is the mounting hub surface deviation, pos or neg, from the centerline of the wheel barrel. An 18x8 +40 wheel will sit more inset than a 18x10 +40 wheel.
18x9.5 with a 38mm offset, stock suspension/alignment, will fit with no other mods. Front may poke just a little but with a degree or so of neg camber, this will bring the wheel/tire back in line of the fender. Rear will fit with a small inset to the chassis.
Tire should be selected to run an aspect ratio comparable or less than the factory wheel/tire overall diameter in order to prevent rubbing. Still yet, tires may rub in the front under extreme compression when running wider width tires.
18x9.5 +38mm - 265/35-18 tire DW, with about 1.5 drop will rub in the rear even with 2-2.3 degree camber. Fender roll will be necessary and bringing the camber back to about 1 degree will make a more flush fitment. 1.5 degree camber in the front will make an inline profile with the fender. Depending on the spring/coilover what have you, compression may/will make the tires contact the inner fender.
If you are going hellaflush, then you want more negative offset, like less than 38mm. Fender rolls and pulls will be necessary and most likely fender liners will need to be modded or removed entirely in the front. More extreme camber will be need to get the wheel inline with the fender. Stretching a smaller tire will be necessary to help prevent contact and to give the wheel that flush look. Negative camber will also be needed.
Caveat - hellaflush is for hard parking only. The alterations needed will make the car handle like poop and thus be detrimental to the intended purpose of the vehicle. If this is your goal and don't care much about the handling and want to simply look good? This is your choice and I will not judge... to each their own.
Look at my journal for my wheel pics.. I'm sure you have already.
Read the tire/wheel tech sticky... I hope you have.