Help With Tire Sizing

[cali-love06]

Ok the time has come to buy some new rims and tires and I am having trouble selecting a tire size for the rims I have picked out. I want to run Advan RS-D Wheel 18x7.5 / 5 x 114.3 / Offset +48 in front and then Advan RS-D Wheel 18x8.5 / 5 x 114.3 / Offset +51 in the rear. I have a Tein Basic coilover setup with a 1.5 inch drop all around. I would like to purchase Toyo Proxes R1R tires but Im not sure what size to get. Any help would be great. Thanks!