1) Under Themes, there is no option to edit — I assume this is because subsites on wordcamp.org are allowed to pick from available themes but not make changes to existing ones or add new ones?

2) I’d like the option of a sticky post on our index.php page.  Usually this is done via a plugin, but there’s no option to load plugins.  Can we load plugins ourselves?  And if not us, can someone administering the main site allow us to run a plugin?

A: There’s no theme editing.

For sticky posts, all you have to do is compose or edit a post, and in the Publish module on the right side of the page, where you see ‘Visibility: Public | Edit’ click that Edit link. You’ll see a checkbox that says ‘Stick this post to the front page.  Then save or publish the post and it will stick to the top of the front page.