Hey All,
I have worked with PHP & MySQL for a while however have never built an actual CMS. I have modified scripts, created plugins for wordpress, etc.. but as I said have never created an actual CMS from scratch.

Here at my office, we have a system for adding leads to a MySQL database and it spits reports back out, say a "Recruiter" has 300 leads, we have different categories we can put those leads in, for example:

[Do Not Call] [Call Back] [Sent Contracting] and so on. Our current system then spits out a report on percentages of each category.

The system is very old, running on PHP4 as of right now. I want to, as a side project build a new system with a current version of PHP, less depricated functions, etc.. and am looking for some tips on where to start, framework to use, etc..?

Is there such thing as a Core, Modular based CMS? Where the core features are present and modules can be created on top of that? What I mean by modules is various "modules" that I can create on top of this framework to get the work done that I need. Such as creating the Add Lead section, View lead section, report sections, etc..

I'm just not familiar at ALL with how to go about creating this from scratch and figured there may be some help out there.

I've completed the redesign part and this may help you all to gather an understanding of what it is I am trying to create. The design can be seen at the following url: http://premier-planning.com/ar-system/new/

Overall, I'm just looking for a little direction or anything that may help me in my new found adventure.

Thanks for any and all responses!