Well, firstly, I know next to nothing about Pullips, so I can't help you much there... The hard body and soft body both have their pros and cons.
As the name implies, the soft body is... Softer and squishier. It's a soft vinyl that looks REALLY nice if you plan to have your doll in more revealing outfits. Soft bust obitsus also have different options for the bust size, while normal obitsu's only come in their standard, medium chested, size.
Now, normal obitsu's look silly in skimpy clothes. They have joints showing everywhere, and they have this weird man bulge down in their lower regions, do to the way their built... The old SB bodies are like that too... The newer SB bodies look more anatomically correct, I guess you could say, but they don't sit quite as easily... Soft bust bodies also stain VERY easily....
My advice? If the doll is going to be in dresses and other full clothing, it's safe to go with the normal, hard plastic, bodies.
As for the magnets.... They're awesome! Obitsus come with a little steal base, and their magnet feet stick to it. As you can imagine, they can pose all sorts of crazy ways with it.
The catch? Magnets aren't going to work through shoes. So if your girl is going to be wearing shoes all the time, or traveling a lot, and not spending time on your shelf, on her stand... No need to spend the money on magnets.
I hope that helps a little, and that someone else can answer the skin tone questions.