I recently saw an exhibition of pastel painting and would love to try this medium. Is it necessary to buy lots of colours to get started or could I manage with just a few sticks?

Starting in any new medium can be expensive and it isn't a bad idea to stick to a small palette of 15-20 colours until you have become familiar with pastel painting. In this way you will quickly learn how to overlay colours, so that they mix on the paper, which is a vital skill to acquire. Then, as all good brands of pastel are sold as separate sticks, you can add to your set as and when you need to.