What a great post! Thanks for sharing this because I think you articulated very well what a lot of people, particularly those who are newer to GTD, can experience. If I may, let me offer just a few of my own observations/ suggestions:
1) Because GTD can resonnate so well with so many people, I think a lot folks often get super excited about setting up their systems which is great but like anything else, you don't want to try and do everything at once. I like to use the analogy of working out. January 1st, everyone is super pumped up with their New Year's Resolutions and is determined to hit the gym every day. They go out and buy all this equipment, running shoes, etc but by February, the "honeymoon" is over.
When I started GTD, I didn't buy any apps/ software but kept it simple and stuck to paper. This allowed me to really get the basic concepts down before going out and playing with all the producticty app "porn" that's out there (and there's a ton!). Learning a new tool while learning the GTD concepts can overwhelm some folks right out of the gate. Treat implementing GTD as a project and focus on one aspect of it at a time before trying to master all aspects (ex. master regularly getting to inbox zero then focus on using contexts. By the way, not everyone uses contexts so if it's not working for you, ditch it for now!).
2) Next, you sound like a very ambitious person with a lot of different areas of focus you've picked for yourself. I'm the same way! I am a musician, writer, manager, blogger, entrepreneur, just to name a few! These are great but can be overwhelmnig. GTD has helped me ensure that I am capturing all of these things in my areas of focus but I don't necessarily have active projects going for each of these at any given time. I have some stored as future projects and review these maybe once a month to see if there's anything I choose to activate. Part of the "stress-free" that is GTD comes from being perfectly OK with what you're not working on at the moment but ensuring it's captured somewhere so that you're brain can relax and give full attention to what you are currently working on.
3) Give yourself time to learn what works for you. I've been practicing GTD for about two years now and it took me a good year to really feel good about my system. In fact, I feel so good about it now that I am able to switch between new toys (productivity apps and gear) every other month or so just to keep things fresh. I am EASILY bored! Don't expect yourself to be perfect.
Hope this helps!
"Life is not the harbor. Life is the boat."