Brushes are tricky to shop for; most of the time, you get what you pay for, but some types are better than others. You'll get a better feel for what you like once you have some experience. From my own mistakes, I would say err on the side of getting fewer brushes, in the best quality you can afford. Plan on spending $5-10 for each brush. This is a particular area where you'll be tempted by the large, cheap, 12-piece bristle set for beginners, but don't buy it. These brushes are not usually very good, you won't use all those sizes and you'll be much happier spending the same amount on two or three carefully selected good brushes. Nothing can frustrate you faster than bad brushes.

In general, brushes for heavy texture paints like acrylic and oil are stiffer than watercolor brushes. You can choose from a range of natural and synthetic fibers. There is a good summary of brush materials here.

I personally recommend the synthetic, or "Taklon" type, for watercolor or acrylic. I would recommend getting:

1) A large flat (or angled) brush
2) A medium round brush
3) A small round brush for details

I have owned the brush in the centre since I was six years old, and have mostly kept it out of sentimental value. However, if you're using your brushes often, you'll need to replace them often. You can extend the life of your brushes by caring for them carefully.