For a simpler experience, use launchers like the ATLauncher or Prism Launcher which can automatically handle dependencies and modpacks.

An in-game guide that you craft by using "Salis Mundus" on a bookshelf. It tracks your research progress.

Thaumcraft has several versions, with Thaumcraft 4 (for Minecraft 1.7.10) and Thaumcraft 6 (for Minecraft 1.12.2) being the most popular.