I think part of your overwhelm is in reading the book and spending one day trying to implement! This is not a quick fix methodology, and as such it will take some trial and error on your part to set up a system that is most appropriate to your needs.
I would focus on making sure you have a physical, doable next action on each of your current projects, and review your lists as often as you need to in order to feel you're in control.
Keep the book close to hand, and I would also suggest buying the "GTD Implementation Guide" if it is available on the DavidCo Web site (it may be a GTD Connect-only offering; I'm not sure). That's a really valuable resource...
This is a very cursory reply to your question, but really there are so many layers to this onion that it can be overwhelming to set it all up at once. Slow & steady wins the race!