The recommendation is 500 to 1500 words, but my experience tells me that a hub should be long enough to cover your topic without repeating itself. As such, some hubs will need more words than others. So long as you write with the mentality that you are being as informative as you can, you should do well.
As for using dialup ... yeah, that should work fine, though it will be a bit slow. I recommend creating your hub info offline and then pasting it online in when you are ready. This should help with the lag a bit.
I hope this helps. :)