I have a 2007 G35X with the Akebono Calipers from and rear, will the following rims fit:

19x9.5 +30 lo disc
19x10 +20 super lo disc

Also what tire size should I run?

245/40/19 fronts
275/35/19 rears

or 245/40/19 all around?

 

Unless someone knows from direct experience with your exact rims, I wouldn't think anyone could tell you for sure. Spoke design is critical; perhaps even more so than diameter. Since you've got wide enough rims for the front, I would suggest you just go with the same sizing all around.; much less hassle.