Good to hear that you are sticking around

You will find MODx to be extremely flexible and there are often many ways to get things done.
Next comes figuring out the links/navigation, creating templates, chunks and the dynamic sections.
This first site will ba a bit more effort but once you get the terms down it is a breeze. Basically you have the following building blocks:
1) Template - HTML file with document and template variables as placeholders for content
2) Document Variables - Placeholders for all the document specific content placeholdres (page title, long tile, content, ...)
3) Template Variables - Extended content variables specific to each document and associated to a template
4) Chunks - Blocks of reusable HTML code that you can use in your template or as building blocks for snippet output
5) Snippets - special resources built in php code
There are also modules and plug-ins but these are more specific so I will let you discover these on your own (and honestly I don;t know much about them yet).
One of the biggest highlights of MODx are the Template Variables (most commonly referred to as TV) which allow you to have custom content setups. Definitely worth checking out.
Here is the documentation:
http://modxcms.com/template-variables.html
And here is a user to user discussion about TVs:
http://modxcms.com/forums/index.php/topic,9989.msg72198.html
Yes you can have the forum as a separate application on the same server.