You want to paint the engine block with hi-temp paint...powdercoat or ceramic will seal the block and retain too much heat. For the head...clean it up really well and leave it bare...same reason.
Exhaust parts (manifold, turbine housing, downpipe) should be ceramic coated...a 2000 deg rated coating. Black is best to keep the radiant heat to a minimum...chrome works well too and looks better than black. A 1500-1600 rated coating will work, but you may get discoloration over time. Color ceramic will always have a lower heat rating than chrome or black. Ceramic will act as a thermal barrier to keep exhaust heat inside the piping...hot exhaust goes out the back of the car and doesn't get radiated into the engine bay.
Air intake parts of the motor such as the intake manifold, intake runners, and intercooler piping will benefit from ceramic. It will act as a thermal barrier to prevent heat soak...The opposite of exhaust applications. Keeps the air inside cooler, therefore more dense, therefore more air for HP. You can also powdercoat these parts.
Almost anything else on the motor (valve covers, brackets, pulleys, etc) can be powdercoated. The downside to powdercoating is it resistance to oil, PS fluid, and gasoline...I've seen it stain over time. It's also easier to scratch/chip.
Ceramic's biggest advantage is it's hardness, but it is also brittle and doesn't take flex very well. Once ceramic goes on...it is very difficult to get off. For most applications on a motor it is superior to powdercoat.
One last thing...ceramic is not a paint. Yes it is applied as a liquid, but that's as close to paint as it gets. Ceramic is a suspension in a volatile carrier...the one I use (chrome) has titanium and aluminum in a matrix of resin/ceramic. It is difficult to apply correctly and MUST have a very clean, bare metal surface to adhere properly...it actually bonds to the metal. It has to be baked at 500 deg to cure.
Powdercoat is really a powder when it's applied. The part is charged with a mild electric current to create static and the powder is applied with a gun producing a kind of "mist". Powdercoat is actually a plastic...when it is cured, the plastic spheres (or powder) melts to form a seamless surface.
Hope this helps.