Re: understanding Mutants and Masterminds
A: Yes they are. You could have 20 strength and 0 fighting, but it actually recommends for the GM's sake to avoid doing that.
B: Yes. So you can have power lifting (enhanced lifting-only strength) to lift heavy objects, in place on both the Paragon and the Powerhouse.
C: The paragon actually has 2 strength. The enhanced strength trait raises it to the listed 12.
D: Whether it can be nullified, mostly, or something like that. Most people don't bother separating them out like the example paragon does, though there are house-rules in which you can't exceed certain figures without enhanced abilities.
E: One is an effect (damage), the other is a power (strike). Look at it this way; strike is a power that is a possible straightforward application of the damage effect.