brake upgrade ....help

i want to seriously upgrade brakes for my 94 tt 2jz. it has those poxy brakes .im looking at some alcons or AP 6 pots. is it an easy job can i use the old disks until i can afford new disks. it says the calipers are made for the big brake rotors 12 5/8 x 1 3/8 inches wide. will this fit on the standard supra rotors . what size are the standard supra rotors ?

You cannot mix and match rotors and calipers. If you are going to upgrade you need to upgrade the whole system.