1) you don't need pre-impregnated carbon fiber. It doesn't have to be pre-impregnated.
2) That's not entirely correct. A carbon mast is very strong in any direction, a carbon hull likewise, as is carbon frames used for all sorts of things. It's a matter of how you lay the sheets, where you reenforce the shape, and so on. In other words, it's a matter of doing a proper engineering job. This won't happen with Apple, though, but at least in theori you can make some extreme (and lightweight) structures of carbon fibre, much stronger, yet ligther than, say, plastics, aluminium, glass fibre or what have you.
There are other ways of making CF rigid than using a core. In fact, when building a hull, even with a core, you use several layers of CF strategically to produce the strength and properties you want in the places you want those properties.
3) That's not correct. It's matter of doing it properly. First saturating the individual sheets, and then put the final coatings of epoxy (or whatever you use) on top of it. In this sense, there's very little difference working with CF and working with glass fibre.
4) You're absolutely correct. And if not painted, or filled with UV-filters, the epoxy will yellow with time.
Edit:
Oh, I forgot to mention, that it's not true that CF with epoxy is no lighter than polyester (which is most often used with glass fibre). Manufactured to be light and with a vacuum (sucking out the superfluous epoxy), epoxy-cf is much lighter than an equal strength polyester (and perhaps even glassfibre, ugh!) shell be it as a hull, mast, frame, plate or whatever.