My answers:
1. Power is rated by bore x srtoke x compression ratio x RPM. Comparing the two, aero engines are way down on RPM by necessity of the prop RPM and they tend to have much lower compression ratios. Compare a Lycoming to one of the more modern Rotax engines. The Rotax has gearing and car type compression ratios and acheives power for much less volume. Also consider the types of cars which were around when these engines were designed. (I know your mate's Porche is a bad example because it's engine is basicly the same design as an aero engine). They produced far less power then. Aero engine developement is hindered by certification which doesn't affect automotive engines.
2. Car engines with carburetters are vulnerable to carb icing. (Actually, hardly any cars have carbs now as fuel injection is the norm as a result of emission controls). Some designs are less than others, and some cars have a hot water chamber in the carb. I had a FIAT Uno which suffered badly, particularly on misty days in the UK when the temp was about 10 degrees.. It had a 'winter /summer' switch on the air inlet which drew warmer air from close to the exaust manifold - a basic and ineffective fix. The guy I bought it from had the engine elctronic management system replaced twice at great expense trying to fix the problem. He looked a bit sheepish when I told him what the problem really was, particularly as he was an RAF Central Flying School examiner and should have known all about carb icing!
3. The range of pressures an aro engine is exposed to is usually much greater than the auto engine, so a lot of manufactureres thought it not necessary to add mixture contol. However, this is not always the case. As mentioned, the SUs and Stromberg carbs did have a rudimentary mixture control, but to be more acuare it was a pressure balance system. This is why MGs with their SUs had a good reputation in the Alps. Some more conventional carbs did have mixture contol. Some of the high end Webers had an aneroid capsule which altered the jet. Most modern injection systems have a pressure transducer to adjust fule flow for ambient conditions. They need it to pass the emissions legislation.
4. Torque is a measurement of 'twisting power' to put it simply. Large aero engines have masses of it - they would have to to turn the prop. Your small auto engine doesn't need so much as it rotates a narrow shaft input to a gear box. However, some auto advertising agencies like to tell you how much torque a car has. It's largely irrelevant unless it's a sports car with lots of acceleration. But torque in a car can be great fun. My TR6 had lots of it!
