Promoting your wordpress plugin
The best way to get your plugin promoted is to submit it to wordpress. WordPress’ extend section gets millions of searches. You can submit your plugin here. You should use the same strategy as if you were creating a post when you submit your plugin. Have a keyword rich description and use descriptive tags to attract as many downloads as possible.
Protecting your backlink on your free template
Giving away free themes are a great way to get back links to your site. One issue is that some people will sometimes change the footer, and you will lose your back link. One way to get around this that I see on alot of free wordpress themes, is that they javascript encode their footer. You can do this by going here and encrypting your footer and placing it in your templates footer instead of your html footer. The end result will be the same.