I appreciate your investigation. For me GTD was something I didn't take on faith. I read more I had those 'aha moments'. I would read something and either simply get it, or try it out and actually see that it made sense in my life.
It has really changed how I feel about all the things I carry in life. I feel more in control...a sense of understanding where I am with things. Don't get me wrong, I still don't do everything I need to...but I'm getting there a little at a time.
Where to start...that's a good one! First, I think it's helpful to acknowledge this is a marathon not a race. It will take time to really get it all...and you will, or at least I did, modify as you go along. I thought I had it all...then realized there was a need to shift and then I had it...well, shift again!
So, to start...read the book. I actually found reading summaries available for the Kindle to be VERY helpful.
Of course this forum is also a terrific place to gather and ask a question or two as you journey into GTD.
I hope it makes a difference in your life too.
iPad, iPhone, MacBook, PC; all running Nirvana, iCalendar and GMail
Mastering Workflow (2012 & 2013)