You need a 15mm socket for one bolt and a 6mm allen head for the other.
Cover the brake pad springs while you tap out the pin, it'll jump far.
You can remove the rotor (after removing the pads) without having to remove the caliper.
The brake piston needs to be rotated (using the two holes in the face.) It will not be pushed in.
You do not need to unbolt the brake arm - simply grab the ball end of the cable and a slight pull will allow you to unhook it. If you must unbolt and re-tighten the arm, hold it with vise grips, since the internal ball bearings have plastic cages that can break when the balls ride up their ramps. Do it in both directions, since the system is left and right-handed depending on side (and I can't remember now which way is against metal stops and which way is against the plastic.)
So, ummm, whatcha doing?