What you need will be very dependent on what you are painting, the size, the paper, and most importantly, your style. I would start out using the soft pastels before buying anything else. As you use soft pastels, you will notice that you may get some sharper edges on the pastel (depending on how soft they are – as soft pastels vary a great deal). If those sharp edges are good enough to create any sharper lines in your painting, then you may need nothing else. If you find that you need some finer lines, then you may want to get some harder pastels. Personally, when I needed a finer line in a portrait or to paint twigs on a tree, I used a harder pastel, but didn’t need to own more than about 5-8 of them (various dark browns, maybe a very dark green and blue). You could also go the pastel pencil route.
Also, depending on what brands of soft pastels you are using, you may find that they are too soft for your initial layer (you are getting way too much pastel on the paper and are unable to add layers on top). In this case, you may want a harder pastel for you first layer.
Conte does make pastels (but I believe they are hard to get in the US) but Conte Crayons are not pastels, (although they can be used together) so they would not be my recommendation. Any hard pastel brand is fine to get.
I realize that I am not really answering your question and making it more difficult! But I always recommend new pastel painters to start with a small set and then find out what they they need before buying additional pastels. People who start out buying full sets of hard, soft, and medium pastels can often end up not using as much as 50 to 75% of the pastels they bought.
Don
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