You can use custom meta fields which is a very inbuilt feature. However, WordPress also allows you to churn out some better looking boxes that are easier to use and better to work with.
A comparison between the paid plugin and the free plugin. Do you really need the paid one? Find out.
Use get_comments to fetch comments. Forget database queries.
More details about Custom Post Types, the new Menu figure and the much expected Multisite / Network (currently WordPress MU)