I like all stamps, but I try very hard to limit my collection to Netherlands, France and all their former colonies and overseas territories. I know that this is a very large number of countries and a huge amount of stamps, but this way I’m always able to find something for my collection.
While most of my collection is mint never hinged, I try to add interest and depth with specialized sub collections and covers showing actual usage of the stamps. I don’t collect anything issued after 1990, and for some especially prolific African countries I stop in 1970.
Currently, I do not use a system to know which stamps I have, nor do I have up to date want lists. I just cross stamps off in an old catalogue. This will have to change (I have some ideas).
I have three different ways of storing and displaying my stamps: large stock cards, Leuchtturm plastic pockets, and Schaubek albums. I create my own album pages using Powerpoint and an A3 printer. You can read more about this topic in this post.
I use specialized catalogues whenever I can: Yvert & Tellier and the excellent Arthur Maury for the French stamps, and NVPH / Zonnebloem for Dutch stamps. It helps to speak the languages these catalogues are written in (French and Dutch). I have additional literature that covers the postal history of the former Dutch colonies, and the Netherlands. I also have many magazines that I’m trying to digitize to save some space in my hobby room.