as many people said here, multisite is one option for you. But... I am not recommending it. The problem here is that multisite is huge hardly managable, have problems with users management and security features. I have lots of problems with multisites.
1) You can have more wordpress sites in one hosting.
Simply make folder on your hosting, copy new wordpress in it, set domain alias and .htaccess to that folder and you are done. You have new, separate site and when you need to get rid of it, you simply delete database and this folder with it. Opposite of multisite, those two or more sites will be separated totally. With this, you need to install plugins separately and do everything separately. Multisite can be managed from multisite settings and plugins together for them all.
2) Custom sites.
You can have more sites on one wordpress. You just need to program it. Nobody tells you that you can not do separate categories, values for separate users and everything. So when you make theme, you can easily do separate theme settings for pages etc. Everything will be in one site, you just need to play a bit around it.
Hope it helps.