Several things come to mind:
First off, if you feel stressed by using GTD the issue is probably that you are not capturing enough stuff or that you are not really processing it well. Once past the initial "oh my, I can't possibly do all this" angst of your first few complete collections of things to do you should feel a sense of freedom when you identify that niggling thing that has been bothering you but now has a name and a space and is finally in a place where you can deal with it when you are ready. That means not only do you capture it completely but that you have processed it completely. That takes time to learn how to do.
For capturing ask yourself
- Do I have a way to capture ANYTHING at ANYTIME?
- Do I like to use the tools I have to capture?
- Do I still feel that capturing something tiny is inappropriate?
- Do I worry about the volume of stuff I am capturing knowing I will never get it all done?
- Does that make me resist capturing ideas even when I can't or probably won't do anything about them now or possibly ever?
For 1 and 2 find things that you like that you can carry with you everywhere, even plan for taking notes in the shower or other unusual places you go.
For 3 know that until you are comfortable your brain is reveling in the idea that it no longer has to remember tiny things because you capture it down. So go ahead, put the minuscule stuff in your capture tool to quiet your brain and leave space for big, grand thoughts.
For 4 and 5 understand that no one will ever get to finish everything on the GTD or any other todo list. The choice is to decide what to work on and when in a way that meets your needs.
For processing ask yourself
- Do I have time to process inputs daily?
- Do I have a good filing system for things I won't do now?
- Do I understand how I think well enough to decide whether I like long extensive lists or short focused ones?
- Do my list manager tools support the way I think?
For 1 Plan on a couple of hours a day just to process your stuff. At least 1 hours and usually for the first few months or year it will take more like 2 hours a day just on processing.
For 2 make sure you use the Someday/Maybe list for everything you may want to do sometime in the future and anythign you cannot do now. The definition of now depends on the answer to number 3.
For number 3. If you get overwhelmed reading a list of things to do to choose what to do that is longer than say 3-7 items then only pick out and keep inactive a few projects that you will work on this week. If you like a longer timeframe (I use 3 months) then you must be comfortable with NOT DOING many of the things on your lists or not doing them right away and you must be comfortable reading and looking at lists with many items on them at a time.
For number 4 that's going to be personal preference. I can tell you why I chose my tool but no one can tell you what tools to use for you.
For the remembering what you have done I'd ask yourself why do you care? Don't the results speak for themselves? If you must show progress to a boss or customer then pick tools that store completed actions and allow you to bring them up again.If it's for longer term personal education then find ways to store the ones that matter. I keep a paper journal of books I've read with notes. Most of the other stuff I don't really care that I completed it so I quit bothering to read it.