I will say that templates haven't changed as much as gear and pets in the last 8 years (if not 12, for the non-gargoyles).
There's only two expansions needed for all content, as everything through Stygian abyss is now included in the base account.
Time of Legends is the newest expansion, and needed for some gear and abilities.
High Seas has added two waves of new content for the oceans, but isn't necessary if you plan to stay on land. However, I think it also includes a storage upgrade.
There's skill masteries for most of the combat skills, not just bard skills. They originated in ToL's Eodon, but are gainable through champ spawns on all shards. Some are better than others.
Pet training is where the biggest changes are, and you need to research those on the Taming board and other sources.
For crafting, the BOD reward system was revised, and most crafting skills have BODs (alchemy, blacksmith, bowcraft, carpentry, cooking, inscription, Tailoring, Tinkering)
Then there's item Imbuing and Reforging (which uses Imbuing skill and the runics from regular crafting skills)