Front/rear disk brake sizing and calipers?

[HellTriX]

Im trying to get the smaller details of my suspension work out of the way now so I can focus on actual suspension setup.

I want to run 18 inch wheels both front and rear in my car, 10 inch wide in the rear and 8-9 inch in the front. This makes me unsure of what size brakes I will need. This is for a 66 impala not exatcly sure of the weight balance but I plan to measure that, was just waiting for the final details in the motor work to be done as it will change the weight a bit.

I'm wanting to use 13 inch rotars in the front with a 2-4 piston caliper (I dont know what size pistons yet). I was thinking of 12 inch rotars for the rear, but then I see lots of other combos that use nearly the same size rotars front to rear.

So I guess what I am asking if there are some formual I can use to calculate a general idea of size of roters and clamping froce of the calipers along with some of the weight transfer etc.

Tnx