Why these characters matter
The anchors worth learning first are the ones with the fewest lookalikes. Gintama has 5 characters, all listed for 2006, where white hair appears on only 1 of them, while black covers 3 — so a distinctive hair colour is often enough to locate the right cluster.
Learn Gintoki Sakata first, then the candidate it is most often confused with: Kotaro Katsura and Shinpachi Shimura agree on 4 of the five clue traits. That one comparison removes the most common failure in Gintama mode.