You will get better feel/feedback over the UK brakes (which I found to be very numb) just by installing a BBK.
I don't run any ABS...I don't even have a brake servo, which means I get very good feel/feedback from the brakes, although my right leg does get a big workout when on track
I wouldn't disable your ABS unless you feel its actually hampering your ability to go quick, from memory the ABS on the Supra is fairly sensitive. That said a lot of racing cars run ABS systems which are designed for racing but those cost ££,£££'s
Don't forget that your tyres also play a large part if not the biggest part in your ability to scrub off speed, the more grip you have the more energy your brakes can absorb, which by then installing a BBK with racing pads will be used more efficiently and effectively.
I find the front and rear kit I have on my track car (KSport) is pretty dam good for the price I paid for them, that said when they need overhauling (and they will probably soon) I will be going to a full AP racing BBK setup as they have more available parts.
If you are planning to run a BBK on the front and keep the rears stock then your brake bias may change. It may be worth looking into that. No good if your front brakes and tyres are doing all the work and your rears are doing nothing and even worse if your rears end up doing more than the fronts (Spinny spinny).