Based on what I've done, and I'm not as low as you can go on BC coilovers, here's my best guess.
18x9.5 ET 45 (~4mm less aggressive than my front setup)
235/40 tires, preferably a brand/model without a square profile
If you want to go staggered you could do a 18x8.5 ET 35 front with the 9.5 ET45 rear. If you liked a wheel that didn't come in those offsets you could run spacers to get there.
Because BCs have camber plates up front you'll have the ability to run similar front camber to what I have now (-2+ degrees) which helps with fender clearance a ton.
What I have now is 18x9 ET45 with 10mm spacers up front and 5mm in the rear, and about -2.4 degrees of camber up front. The only thing I've done to my fenders is to bend up the little lips at 2 o'clock and 10 o'clock where the fender meets the bumper, I was getting a little rub there on a hard freeway speed dip. No rubbing in aggressive driving. My car sits about 25" FTG (fender to ground).
https://www.willtheyfit.com/index.p...2=40&wheel_size=18&wheel_width=9-5&offset2=45
IMG_20180207_223008_149 by
Jon Collier, on Flickr
If you want to run more tire, I'd think you'd need fender work if you're going much lower than I am especially.