What 1000 email accounts means is that you have 1000 emails at your disposal. Usually how most web hosting compies work is this...
You have up to X number of email accounts. If you do not use all of them you DO NOT lose them.
For example you said that you wanted to use only 1 email. You will have 999 to use at some future time. You may want to check with the hosting company, but usually they have a way that customers can create, edit and delete email accounts as needed.
Hope that helps.