You need a list of Projects, lists of Next Actions, and a place for project support material. Most people starting gtd have some system for project support already. If it’s working and it suits you, then there’s no need to change. Most people start out pretty disorganized, though. I use a digital tool (Things) that is adequate for almost all of my project support needs, because it can hold small npbits of information in notes fields, and can link to email and files. Other people use papers in folders and do very well. There’s no one good choice. The one thing I would not recommend is planning next actions too far ahead. Change happens and your planning is obsolete. Worse, your subconscious will know when the steps are all wrong, and send messages to resist doing the project. With experience, you will learn when and how to plan better, and when not planning is better.