Hi, The wordpress is such a great tool. I'm wondering if it will be a problem to start adding sections at some point, nothing to do with the blog, just sections for the site with different functionality ( say a database of searching stuff ) perhaps also incorporate and let user reistered through the word press database with the other featues in the site?
What should I need to know for this? will it be OK?
You can modify the wordpress pages if you want it integrated in the blog, or add new things on other pages.
Are you asking if you can use the wordpress login info for other sections of your site?
Some firm knowledge of PHP will allow you to write your own Wordpress plugins,
see this (Wordpress: Writing a plugin) page for more information.
There is also a 5 minute video tutorial about writing your first plugin which can be found here
You should try PodsCMS as a way of expanding on top of your vanilla Wordpress install. It's got a great interface, great tutorials, and the developers are always more than willing to help.
You can literally do just about anything with PodsCMS, especially with a good working knowledge of PHP and WordPress' workflow.
I've found the Wordpress plugin Magic Fields really useful for adding cms style features on Wordpress Pages. It may give what you want.