seriously, if a book is less than 250 pages, it feels like it's finished before you start. If it's over 600, it feels interminable.
At least when you are dealing with actual publishing.
If you plan on doing a webnovel that may eventually get published, it can all be one book... but having the occasional break where you let people know that the actual book would end can help them offer suggestions for getting things pounded into order.
If you are doing a webnovel for sponsorship? Don't bother dividing it up. You can have a plot thread that doesn't get resolved for 500 chapters, just remember to keep a list of ongoing plot threads. web readers DO like seeing problems resolved, but you can take your time as long as you keep them entertained while waiting for a particular denouement.