18x9J+25 and 18x10+40 114.3x5 ...Will these bad boys fit on a z?

 

They should, my rears are 19x10+40 so I don't see why your 18's wouldn't fit.

 

They will fit but the rears might look a bit sunk.

Your ideal setup would be

9" high teens, low 20's offset and 10" in a mid 20's to low 20's offset depending on tire size.

Naturally basing this off a 245 front and 275 rear.