Thank you for all the replies.
The concept of having a "project support" list was something that have somehow slipped my mind when I read GTD. I am currently thinking about implementing GTD in Evernote only, because I know the software, it is quite simple, and available on windows/web/android. And at the moment I want to focus on implementing GTD in my life, and not on smart software. Once I am in the habbit of using GTD on a daily basis, I might consider migrading to other platforms. In Evernote I will use tags for project identifications and contexts, and I will have notelists for Inbox, DataReference, Somday/Maybe, NextActions AND ProjectSupport.
I agree that future actions in a given project can sometimes be quite unpredictable. Therefore I think it is good idea to be flexible, and accept that in some projects the future actions are being defined "along the way", while some projects are more static, and can planned step-by-step from the get-go.
I have just started doing a brainstorm, to identify all the "stuff" in my life, and will dump it in my inbox for processing. I have a lot of free time this weekend, where I hope to be able to get through my intitial inbox. I have an idea that this will take quite some time.
I will look into www.afterthebook.com and www.thesecretweapon.org before starting my own implementation.
Once again, thanks!