Wordpress is a tight little CMS, especially for articles, but it is a pain in the butt making your own theme the first time around. (this is especially true for those with no HTML, CSS, and php experience.)
1. Here's what I learned from editing my own wordpress themes. Maybe I'm stupid and clueless, but I could never figure out how to make my own theme, so I just edit the default theme. This is geared towards people with web design experience.
You can edit your wordpress CSS through the wordpress panel, but I download all my files to the hard drive and edit them through dreamweaver. Then I upload through the FTP route.
The default theme's files can be found in wordpress > wp-conent > themes > default. Everything in wordpress is modular, so you really only have to edit a few files (index, header, sidebar, footer, and style.css ) to begin putting your new theme together.
If you're designing custom graphics for your WP, then try to keep those files in mind... it helps first to understand how they're all put together. Wordpress.org documentation is very good though, so anytime you need help with something its worth checking out.
2.) I know there is an adsense plug-in out there, and I'm certain there are plug-ins (once again, check out wordpress.org:
AdSense-Deluxe WordPress Plugin » Acme Technologies Zeitgeist) .
Basically you tie your ads to certain code, like <!--adsense01--> and plop it in when you write your article. You could also hardcode your adcode when you're designing your template.