Yes, Mustangs have a tendency to be built into all sorts of varieties, according to the owner's wishes. It's what makes them great -- and sometimes confusing and a little fake.
Yes. The S550 is good and bad in my opinion. The build quality is up, but so is the weight. Stock for stock, sure, it handles marginally better than some of the previous versions, but I don't quite like the weight increase.
The ecoboost version is very interesting, the V6 is plain boring -- as always, and the V8 is as good as when it debuted in 2011.
As for motors, the modulars are actually rather good. If you will remember, Koenigsegg used to run the old 4V in the CC8, before they switched to their own design, which even then leaned heavily toward the modular architecture.
The newer 4V versions have all been great -- especially with boost. Modulars really need boost to shine. The 3V I have a soft spot for, but it does have notoriously weak rods. They don't last long. The 2V, however, is forgettable.
People seem to dislike the modulars due to the inherent problem with cost; it's much simpler to take an LS based engine out of a truck or van, throw a turbo on it, and make 800.
Here's a good, albeit little extreme, example of Modulars versus LS (noticed the header design on the winning, 4V engine):
Jon Kaase Racing Wins Amsoil Engine Masters with 409ci Ford - EngineLabs