I run TRP Spyres on DCD with post mount to IS adaptors. You can use the same calipers and rotors for the front and back, but you will need adaptors of different size. If I remember correctly, the reason is that by default IS implies a 140mm rotor for the back and 160mm for the front.

As said, flat mount is a different story.

If you can go hydraulic, go hydraulic. Do not be shy of it I run cable actuated brakes because I run 3x9 as a heavy rider.