Take a look at the .tpl files under the install/assets/ folder for guidance on how to create your own .tpl files for chunks, snippets, plugins, modules, and templates. Make sure you place the accompanying code in the appropriate folders as well (i.e. if you want to include PHx, create a .tpl for it and also put the PHx files in the appropriate folder).
As for template variables, there are no examples. Look here:
http://modxcms.com/forums/index.php/topic,47933.msg281353.html#msg281353
I install regularly used components, including all my blogging stuff, google map, seo template variables, etc. It’s great and saves a lot of time.