Themes are for the “look and fee” of a WordPress site while plugins are for adding new features to your blog.
Themes should not add extra features to your WordPress site. Themes should just control how your site looks, while features that you want to add to your site should be from plugins.
That way you can change your theme in the future without losing any of the site features that you’ve added.
For new blogs the content is much, much more important than how the site looks. A blog with a lot of great content on an ugly theme will do better than a blog with a really pretty theme but not much content.
When you’re still new to blogging it’s a good idea to pick a free theme you like right from the WordPress admin dashboard Themes page. Use that theme for awhile until you get a better sense of what you want from your theme.
Once you know more about themes and what you’d like from a theme, then that’s a better time to invest in a quality paid them that includes all future updates for one price. Once you’ve paid for a theme you have the right to use it on your other WordPress sites, too (if someone says otherwise they’re ripping you off).
I like using Genesis themes. They’re designed so you may customize how your site looks while getting regular security updates that won’t change what you’ve customized. The updates are included for free.