What I try to do is not work hard and let up, but rather start working ahead of time at the pace I intend to keep. When I have a couple of weeks in the can, I strive to write at the pace I'm publishing.
What I've found is that writing a serial is very different from writing a book. It's actually more different for the writer than for the reader, really. (A reader, after all, can wait until the serial is done and then read it as they would a regular book.)
The thing that might hang you up is the ebb and flow most novel writers have. Sure, you may train yourself to turn out 2000 words a day -- but because the thing isn't done yet, you have the unconscious freedom of having on-days and off-days. Sometimes the prose is rougher than others. Some days you know where you're going, and some days you feel your way along. Some times you'll write like a demon for weeks, and then you'll crash.
Writing a serial is more like newspaper writing -- or performing. Even when you give yourself a buffer, every day still has to be an "on" day. It is thrilling, it is exciting, it is wonderful... and it's way more exhausting than you think it is.
Which is why I love it.
I'm working harder doing two 600 word episodes a week than I did writing over 1000 words a day. (Of course much of that work is related to the incredible shortness of the episodes.) My buffer rule is to have a good outline for the next 8 episodes or so, and try to have at least 4 drafts in the can -- and then I have to write at the same pace I publish. No slacking off. Also, I didn't start by writing a lot really fast. It's not good to sprint at the beginning of a marathon. I just didn't start publishing it until I had the buffer I wanted.
As for whether 2000 words is too long? There is no rule book. We're inventing this thing as we go.
My advice is that you have to find your length. It may be a negotiation between the goal you set and what the story wants, but after you've got a number of episodes under your belt, you'll find that your imagination starts building the story in "episodes" with the appropriate amount of story in each. It becomes the voice of the story, and IMHO, at that point, you can freely let the story rule how long the episode is -- some will be a little longer, some may be shorter.
I'm writing short specifically because I'm aiming at the idle browsing audience. I want mine to be more like a comic strip than a novel. Not so immersive. But that same idle browser could as easily be attracted by a spiffy headline or a great opening paragraph, or artwork or any number of other things. People read long things on the internet all the time.