Moved you back to the General Section. I agree, your topic is not security specific.
I started out with just thinking about basic security; doors & windows.
Once that was done I thought it would be nice to have security cameras monitoring my home 24/7.
After the security was set up and the infrastructure was in place, I now wanted to make some lights automated.
Like most, when the automation bug bites I couldn't stop until every light in the house was automated. That's when the whole set up had to be software controlled (AHP).
The final major stage of my system was now to have full control of my home and access to cameras from my laptop when not at home.
The last stage for me is the bells & whistles, tweaks, updates, etc. This stage, of course, has no end in sight.
If I were to start all over again, or even make a recommendation to someone starting out, I would take a more top down approach as opposed to the bottom up as I did. You could still do the small parts in the order of your personal priorities, but start by thinking what you would like to be the finished system. Then break that system down to the smaller sections and determine the best way to implement and integrate it. I know I have done many makeovers and have lots parts that I no longer use, just from changing what I had done to make it work the way I wanted in the end.