Category navigation

when having more than 20 main categories the navigation box become too big.
I think category should behave as manufacturers, maybe add a categoryNavigasion property like homePageCategories.
further, there should be a catgoriesAll page

If you consider 20 top level categories too many to display at once in the category navigation and you would consider marking some of those as not to be displayed I would contend that you have too many anyway and that you need to reconsider your information architecture. ie reduce the number of top level categories and/or recategorise and/or add another level of categorisation.

HTH

However as an alternative you could use Category templates and filter category navigation similar to this (note code has changed in 2.7/2.8 so you would need to rewrite.)