Denser air means you need LESS power to stay airborne at the same weight.

Hot air is less dense than cold air.

Moisture adds some density.

elevation above sea level has a large effect on density (higher above sea level... less dense.)

Generally... if you are close to sea level the minimum size of the recommended engines by the airplane's instructions will be just fine. (Yes I did say that!)

If you are well above sea level then you will tend to need more runway for takeoff and landing. or some way to get more thrust, or you have to lose some weight. usually just shifting to a longer lower pitch prop helps a lot. At elevatons above 2500 ft... you usually need a bit more power to swing an even bigger prop (the max size engine listed). By the time you get to 8,000 ft above sea level you are wanting more nitro... and a bgger prop and an even bigger engine. (if max says .46... you may actually want about a .60)

REally though... even at the 8000 ft level the plane WILL fly with the minimum recomended engine... it just may have very poor performance.

You CAN get passable performance just by using a different flying style. (Unless you want to hover that 30% Extra 330 L you are dreaming of...) Then you really do need more engine at high altitudes.

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You notice I didn't say anything about temperatures related to engine choices above? Well... the density altitude problems that come from higher temperatures are almost always associated with flying from higher altitude airfields, on HOT summer days. (some airliners can't get out of Denver more than half full on a "warm" day.... but have no problem full loaded at the same temperature taking off from Hawaii fully loaded.