Capability similar to Wordpress Custom Fields?

Hello,
I’m going to be running a website that displays a gallery of products on other websites I have been using Wordpress for the past two years, and I’ve been using Custom Field Plugins. With the custom fields, the "create post" page has a custom field for the link to the product, the price, a place to mark free shipping, the merchant, etc. Is there a capability for that in Modx?

Also, is there something to place the most popular posts of a certain week onto the main sidebar and continue to replace the list with the top most updated posts?

I’ll answer quickly:

1. Explore TVs, "Template Variables" for custom fields.
2. Explore Ditto and Reflect snippets for auto-updating list.

If you ever need help, feel free to ask in respective forums.

Wow, that easy, huh?
Also, how advanced are the community features on ModX? I’m not looking for super-advanced features, but I would like users to be able to create accounts before they post comments and integrate user accounts into a forum?

Seamless integration into a forum is an area that is currently not optimal.