I have been using Scrivener in its Windows guise for over a year. I had been a keen trialer of writing software, actually purchasing a number of packages which seemed to fit the bill in the moment. I could recommend Power Writer/Power Structure package if it were simply a novel. Liquid Story Binder is a very cheap package which you can tailor to your own preferences. However, pound for pound, I reckon Scrivener to be the standout package for any kind of writing project.
You can use it straight out of the box without fear of mishap, and learn what it has to offer as you write. I average 3,000 words a day and, after a year, I am still discovering something new and exciting in its box of tricks.
Its great strength is in its ability to bring order and logic out of the chaos of written scraps and pieces I accumulate; and in its ability to provide writing space at any point along a story arc.
I note that you are a mind mapper. Have you tried Personal Brain? There is a wonderful free version, although I have used the paid pro version for over three years. It is a spectacular research and note-taking software which links all your material in a logical but not linear way, highlighting the unseen links in your research. I mention it as I use PB to research and outline my work in a mind map format and then do the actual writing in Scrivener. I'm sorry if this feels like salesman's blurb, but you did ask and I really feel compelled to sell a product which I have found to be invaluable.
Good luck, and if you have any questions, please be in touch.