It depends how important your CMS is going to be and your skills to do it. If it is not very important then you might want to adventure yourself and develop your application, otherwise you might want to hire someone.
If it is a simple application, or a common task, chances are that there is already something developed for your desired functionality. CMS is not a must for a web application, but many have thousands of plugins for them. Try searching the extensions in Joomla and see if there is one that suits your needs http://extensions.joomla.org/
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First of all, you should be familiar with web application environment if you are going to develop a web application. CMS is not compulsory but most of the developer prefer it specially Joomla to avoids further bugs during development of a web application.