There is no such thing as 'perfect' security - there is always someone looking to find a sneaky way to change what you had in mind for your WordPress installation.
Do yourself a favour and install this plugin.
It isn't perfect, but it is about as close as us non-security experts are likely to ever get.
Feature rich - but not daunting to use and there is an active forum, and a worthwhile mailing list (this review posted on 18/04/13 and the most recent mailing included tips on how to mitigate the global attack on WordPress sites)
As you progress you may end up wanting the extra features of country blocking etc - which are paid for - or you may just think that it is so useful as a free plugin that you are going to pay the small annual amount to support the developer.
I rarely comment on plugins - but this is a must have for anyone with a WordPress installation.
Be wise - install Wordfence