If you use Joomla, you are familiar with some of it’s benefits, and short comings. The built in banner mechanism supports banner rotation (useful if you wish to attract advertisers), and the user/contact manager, while not as deep /flexible as some of the other CMS, is relatively simple and has several levels of control. and the end user interface seems relatively simple. Among the designer drawbacks, has been the necessity to delve into the core to alter some of the layout, and the section/category limitations.

The category issue has been addressed by a large number of extension and programs which list some form of unlimited levels, nested, or many to many categories as part of their features.

Joomla-knowledgebase.com
mightyextensions.com
www.vistamedia.fr
Accordian Menu for virtuemart
joomanager.com
K2

There are other extensions and other ways to add category depth, and the links above are not an inclusive list or recommendation, merely a starting point.

However, if you sure one of these programs, remember that open source (Joomla, WP, Drupal) CMS cores are constantly in flux. When an outside extensions or custom interfaces are used to modify the main CMS software, when it is time to update, there is a chance that the extension based modifications will fail. You have to hope that the extension maker has updated his software to accommodate the CMS update, or that there are no CMS structural changes that break the hooks used to make the two pieces of coding work together.

If you work within the core components, the upgrades usually let your site survive without major revisions. To my mind, that makes a single db, with a single install & ability to upgrade better than heavily altered cores with custom extensions.

Before you create custom interfaces, install third party hacks, or pay for custom coding, check out what is being developed by your core CMS. The major open source programs are supported by large and active developer bases, while most extensions are the work of one or two people. Unless the extension has a long track record, and is dedicated to working with the CMS, you are
risking the Update Dislocation Blues.