Correct a 19x10.5+12 with a 305/30/19 tire will not rub... You could actually bump it out another 10mm and it still wouldnt rub with normal camber.
Remember the Z is already set from the factory with negative camber so when you get it aligned it will probably be at around -2 which will camber in a little at the top AND the 370z has rolled fenders in the rear from the factory so no worries my friend about rubbing.

19x9.5+25 front you will not rub either with a 255-35-19 tire.

^ right on !

how about 285/35/19 on the front? i feel like the front will get left behind in terms of tire meat since im gonna be running 305s on the rear. you think im gonna rub? or maybe 265s? i already read the whole meaty tire thread on here. i saw a picture of a 255/35/19 on a 9.5 wheel on the front and it seems like it could use a little more tire meat.

You can't run a 285 up front wayyyy too wide.
If you are rocking a 9.5 inch wheel the widest I would go is a 265-35-19 BUT a 265 is taller then a 305-30-19 (not by much) but its like .1-.2 inches taller.

A 255 front and a 305 rear is perfect. Stay with that combo... There's a reason that's the most common tire combo 370z guys are running ;)

i think im going with 265/35/19. so what does the 0.1-0.2 inch difference do? any disadvantages?

Well I believe the VDC/TCS may react slightly different, with that slight of difference it probably wouldn't cause any issue you would notice on the street so I wouldn't worry about it... Personally though I wouldn't ever want my front tire taller then my rear tire even if it is only .1-.2... But that's just me

I have had 245,255, 265 on the front of my 350z before I got my 370z.... Personally on a 9.5 inch wide rim I think a 255 fits it the best. A 265 looks squared, 255 tapers in just slightly and a 245 has a slight stretch look.