Kim,
this article may help you understand the different types of paper and how they perform. It really is down to personal choice as to what type you use and of course what effect you're looking for too. Some like a rougher 'tooth' to the paper as it holds more layers of graphite or coloured pencil etc.
The weight of drawing paper (or watercolour, etc ) is determined by the number of pounds in a ream (500 sheets) of paper. The more weight, the thicker and heavier the paper is. An average drawing paper is anywhere from 60 - 90 lbs, meaning that a ream would weigh 60 - 90 lbs. An average watercolour paper for instance usually is 140lbs.
Experiment. Buy single sheets of paper and try them out if you can. Different mediums, different supports...I'd say there must be at least 9 or 10 different types of paper on my art storage shelves. And if I see something interesting, I'll buy it and try it out.
As for using black. Well the reasons have been laid out for you. But of course you can use black and we all do - when its appropriate. Black should NEVER be used for shading, as shadows aren't black at all, they're composed of all the reflected colours of the surrounding environment. You can use black, but always soften it with other colours in the palette that you're using. It will create a rich, deep black that has movement and interest. It really becomes a boring colour if used on its own and is flat - almost like a dead space in your picture.
Touches of black work in many drawings, but they usually are touches, not large areas. I'd suggest that you get out a colour wheel and do some exercises in creating colour swatches - little blocks of colour - using a variety of pencils or paints and see the range of darks that you can achieve without even considering black.