New disc brakes for my 2004 corolla

My 2004 corolla needs a new set of discs, pads , calipers, because the discs are too thin (20.4 mm vs 25mm original) according to uttam toyota, noida.

can i still grind them ? because brakes are too weak now, probably due to the lines on the discs.

toyota service center gave me an estimate of 16k, all inclusive, for 4 discs along with pads and calipers.

can i go for bigger – aftermarket discs in a nearby budget ? without compromising the ABS.

Are the ABS values tuned to each disc rotor size ?:OT