I believe that Spandorexxxa's hair is quite long. One thing to consider is that your hair is probably going to be about 1/2 the length when it's dreaded. As the dreads "knot up", they're going to shrink.
Dreads do stay wet longer than undreaded hair. I haven't heard of them growing mold, though.
I would think you'd be able to do a few dreads as opposed to a bunch, but you'd have to pay close attention to them on a daily basis, especially when you first do them, since they could attract more hair and become more of a mat than a dread.
Really, your new dreads are going to require a lot of maintenance in general, whether you do a few or your whole head. Especially in your case, I think I'd try a few synthetic dreads/falls and see if you like the look. I think in super long hair the dreads would look really good, but they're going to be murder to put in. You'll need a friend with a LOT of patience!
As for dying (please correct me if I'm wrong), you're really only dying the outside of the dread, but when you color, you're going to squish the color around and then rinse very thoroughly (while squishing) in order to get ALL the color out. I think it's a little like cleaning paint out of a paint roller/brush. Wash, squish, rinse, squish...repeat.
I'm not really sure if bleaching is really recommended. I'm sure you could do it if you are going to be super careful when coloring/rinsing. I'd be afraid of breakage, though, I think.
If you do the dreads, let us know. I love dreads myself and have considered them. I just never let my hair grow long enough (and fear that work would FREAK).