1. I've got the idea for an addon which gives a message whenever a tracking of some sort is coming in.

    More detailed, I want to get a global message much like the "no flying zone" when flying in dalaran, whenever I find, lets say, an herb or an ore deposit.

    However, I cannot find the right thing to track for updates (no incoming_track widget, event or anything)

    Anyone know what I should look for?

    Blizzard purposely gives us absolutely no information about items that are trackable or tracked on the minimap. There's no (easy or feasible) way to find out when a new item has appeared within your area of interest.