Having code design trouble

I've been trying to design a blogging system recently and have been running into some snags on my design. It may be due to the lack of knowledge for PHP development and/or web interface development. I'm attempting to take the MVC pattern and apply it to a simple yet powerful blogging system. I'm trying to design it where it will allow for plugins and themes (or templates) whichever you prefer. While I'm typing this I'm trying to think of how to design this type of system without getting in over my head on this. I'll probably run into some unforeseen issues which I really hate because some issues may require me to recode a lot more than I want. I know I want to stick to the MVC pattern and I see some of the user interactions that may occur but their may be more that I'm not aware. So I guess now the issue is my design good enough to handle such things. I really do hope so. Well... before I start coding again I think I'm going back to the drawing board...