For the best cooling, you want a decent sized A rated Power Plant with a G3 Low Emissions Power Plant, and you want the heat efficiency number to be as low as possible (IE 0.2-0.3). This will increase mass and reduce output however. If you want a smaller/lighter/more powerful Power Plant, try G1 Overcharged with a decent Heat efficiency (0.41 or lower)
For Light Years you want a good FSD (of course), and Lightweight Life Support, Sensors etc. If you're out to explore, it's also recommended to lower the size of your thrusters and giving them Dirty or Clean drives modifications to completely max out your jump range while maintaining the ability to land on planets.
For Light Years you want a good FSD (of course), and Lightweight Life Support, Sensors etc. If you're out to explore, it's also recommended to lower the size of your thrusters and giving them Dirty or Clean drives modifications to completely max out your jump range while maintaining the ability to land on planets.
Maybe also give G1 low emissions some tries, heat efficiency normally drops to around 0.32 to 0.3 and there's often only a minor penalty to power output and sometimes even a gain due to side effects. All in all it's a very well spent piece of iron... 
If you size it too much down, yes. Just fiddle around with modules in Coriolis or edshipyard to try the best combos