I believe your front wheels will rub, as our fronts are already quite close. I'd certainly stick with a 255 or smaller tire if I was going to run that aggressive of a width and offset. The 10.5 +18 with a 285 does rub just a bit on our car.
Aggressive offsets are always a bit hard to judge, as exactly how everything will fit will largely depend on the specifics of your exact setup- wheel pad height, true tire section width (advertised width is rarely exactly the actual width of the tire) your car's camber settings, etc...
You can fit a 19x9.5 +17 and a 19x10.5 +18, but you're going to have to be willing to adjust ride height, camber, and tire size to fit offsets like that.