On number 1 - you can set up the list of ""alternate items"" and that can appear for an item but not a pop-up.
On number 2 - I advise people to set up their tree in an outline style, meaning the high level categories are 05, 10, 15, etc. Then sub-categories of 10 are 10.05, 10.10, 10.15, etc. Then have subcategories of that as 10.05.05, 10.05.10, etc. Keep the numbers with spaces in between so you can add things in the middle.
On number 3 - never seen this before.
On number 4 - Traditionally I've seen IE being the ""supported"" browser although others do work.