I tried doing the "words per day" and found that I was either getting the quota, or writing mindlessly to meet it. I found quality over quantity works much better. Sometimes you do have to unload all the creativity, but I've found time is better spent putting something out that meets my quality standard rather than some number. Time goals seem to work better for me, especially when I'm "not in the mood". By the time the timer goes off, chances are I'll be in the mood to keep writing.
I'm not sure you can really put a word limit on how much you should write in a fixed period of time. I understand that it's a sort of self-discipline technique you're attempting and if that actually works for you then don't let anyone mess with your style. For me, I write as much or as little as I can when I'm in the creative 'mood.' Some days I don't write anything, some days I simply make notes and some days I can sit down and pump out a few K. I don't think there's a wrong or right way but if you push yourself for quantity instead of quality, you may face the world's worst drafting process. Good Luck
I don't think it's too much. As long as you realize what you're getting into. I like doing nano each year but it is a bit draining and that's only 1667 words a day if you stay on track. When you get behind, it's a pain to catch up. I tend to do betwen 5 and 10k a day for a couple of weeks because I never really do the everyday thing and defeat the purpose. But it's doable, if you realize that some scenes are going to be easier to write and some scenes will feel like an eternity later with only a couple of hundred words.
