What?
I will define reading smoothly as being able to understand on sight 98% of the words on pages aimed at average adults. I know from Spanish that once you hit that 98% point, you actually can figure out most of the words by context, or at least get through the text with one or two quick glances at a dictionary. Anything below that is pretty much tortuous for me. I don't have a personal tolerance for the not-knowing.
Wikipedia articles are a good benchmark. Novels for a general audience (not classics or "literary works") also fit. Though I want to read some classics, that kind of reading is usually very arduous, even for languages where you are a native speaker.
How
When I finish my 1,000,000 word challenge in Spanish, I am going to cross it off the list. I am probably at the 98% level in reading right now, but I am going to hold crossing off a finished goal as motivation for my challenge.
I have a large personal library of Spanish books and the public library has a good selection as well. Finding interesting stuff to read, even more my picky tastes, is not that difficult at all.
I own 7 physical books in French, and will let myself supplement that number when I get to French. Also, by some miracle, I own 3 printed books in Dutch. Lastly, there is quite a bit of good materials available for free online in all three languages.
Since I have an obsession with thinking about methods, and organizing those thoughts, I will present the extended version of my plans:
First, while finishing the previous language, I start playing with the next one on Memrise. I find the only thing I like there is the "no typing courses." When I hit the winter of feeling comfortable with a language, I will switch to doing a tweaked version of Iverson's wordlist method. I did a trial run with it on some Dutch words, and found it much more time efficient, or least far more pleasant, than doing a memrise course that requires typing. Also, it should be noted that my goal is really reading only -- I want the best version of people's ideas and I have no desire to pump more small-talk into the world, especially in another tongue. With enough words, you really start puzzling out texts, even if your grammar is far shakier.
After 5,000 or so words in this method, combined with 2,000-3,000 words and sentences from Memrise, I will start reading parallel texts as soon, moving up from children's literature to more and more authentic, grown-up texts. I am going to do this first in Dutch, then in French.
When
As long as it takes. If my wife and I have a child, then my focus will clearly be elsewhere. So I estimate that this could take 10 years at the maximum, and 2 and a half at a minimum. We'll see.
Where
Just at home. I really don't like travel. I wont be chatting online. I will keep getting conversation practice in Spanish, so I do plan on being bilingual, but after that I am only working toward being poly-literate.
Why?
It's fun. It's good for the brain, and looks as impressive as nearly any of the other bucket-list goals.
No, seriously, why Dutch?
I heard it was easy for an English speaker to learn, so I have played with it in the past and saw I liked it. One thing I really dig is how the "g" makes a very phlegmy "hhhuuu" sound. I like how Dutch has more agglutination than English (without going all agglutination crazy), and I like how it as least gives me a taste of the Germanic side our language (and sure, I might learn other Germanic languages one day as well).
Dutch is a really fun language that deserves some of my play-time.