Yes, you can! When creating your project, you'll have the option to add rewards. When adding a new reward, you'll be asked the question "How many are available?". Here you can specify a number or tick a box to make the reward unlimited.
For example, if you want to offer 10 signed books, you can limit the reward to 10. As soon as 10 people have pledged for a signed book, it will be marked as sold out and supporters won't be able to select it anymore.
You are also able to add options to your rewards. For example if you were offering different sizes you can add small, medium and large options. You can type whatever you like in these option boxes..
The quantity relates to the reward as a whole, you are unable to put quantity amounts on individual options.