I think Wordpress would be a good idea because
- it is open-source and widely used (estimated 17% of the interwebs!), so there will be loads of support should you ever have any question about it
- it is blog software, supporting all kinds of topics (categories), articles, comments, users, tags, templates, plugins and an excellent administration interface
- there are already thousands of thousands of plugins that will suit your needs for other components of your website
- it is easily extended to handle "custom post types", an entry of data with a title, content and other attributes that you can define yourself
By writing the specifics of your website as a plugin you can easily update any Wordpress part of your system (and ofcourse your own php files)
Wordpress comes with an option to queue a comment for approval by a moderator or administrator, you can use this. If you want the order of the comments to be of importance, you could achieve this through a plugin. In Wordpress, comments can be nested in another comment too (a reply on a comment, so to say).
You can handle the interface aspect (sitemap, old school design,) through a template, they are not dependant on the system you're using if it's any good.
Like always, learning the mechanics of a system can be quite a challenge, but you'll find WP is well documented in the codex and is not all that hard.
Good luck!