You don't really have to know the core , If it serves your purpose.
Content management systems.Especially popular ones are very complex.The code is divided into hundreds of small files.
I personally think it's unreasonable to bypass regular functions and write your own syntaxis(somewhat) like Joomla.but that's not my problem.
All in all if your website is small,content management systems should either be very light,or don't use them at all.
To be quite honest,I'd take your design over any other overly-crowded,bright,unbalanced template.
The only thing you might want to reconsider are the buttons.I'd put them a little more to the right of the logo and make the borders one idea brighter,but then again maybe that's just me...
If you need help with PHP and MySQL give me a shout.