hi guys, the question is will the 406 rear calipers,disks fit on the 405 rear brake system??, will the 405 abs system work with the 406 braking system??

IMHO the stock rear brakes are usually well suited for any application, given good rotors and pads, unless you plan on pro racing.
so i would recommend uprating the front brakes, the master cylinder and servo.

p.s. the 405 ABS reads from driveshafts on the front axle and from the bearings on the rear axle, so unless you plan on changing those bearings, the ABS sensonrs should work fine.