I'm not hugely clued in about what to use for graphite and charcoal, but I can help with pastels.
Generally you don't really work with gsm for pastel papers, its more about the tooth than the weight. I work on velour, which is not toothed, and so **** hard to work with - once the pastel is on, there is no fixing it. The toothed papers like canson mi-tientes are fairly forgiving, and you can vacuum or lift off the pastel layers to alter things. They also hold onto the pastel quite solidly, where as velour is extremely delicate.